ASME Conference Presenter Attendance Policy and Archival Proceedings

2013;():V002T00A001. doi:10.1115/SMASIS2013-NS2.

This online compilation of papers from the ASME 2013 Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS2013) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Mechanics and Behavior of Active Materials

2013;():V002T02A001. doi:10.1115/SMASIS2013-3040.

Passive control of cooling processes is in designs best interest. Coolant medium flow to hot components must be kept at minimum acceptable level from lifting perspective to achieve maximum process efficiency. Required cooling of the hot components depends directly on engine power setting, which in general requires a relative complex system for monitoring critical parameters and adjusting coolant’s amount with engine load. Concerning the operation reliability, pseudoplastic shape memory alloys offer a high simplicity in the design of adjustment mechanisms with large operating displacements. As the shape memory effect is induced by temperature changes, the behavior of shape memory actuators and therefore the coolant’s amount can be adjusted to the load conditions of the engine by using appropriate shape memory materials. In this paper an actuator based on a shape memory membrane using the extrinsic two-way effect is presented to vary the cross-sectional area of a cooling air channel with respect to the engine operation. The reset of the mechanism after one temperature cycle of heating and cooling is realized by using a leaf spring element, which is in varing mechanical contact with the shape memory membrane depending on the hysteresis of the entire system. Maximum displacements of the system are attained for spring forces between the force generated by the shape memory membrane in the martensitic and austenitic state. Thus, the system mechanism exhibits two non-linearities of pseudoplastic shape memory characteristic and contact mechanics with friction. For this purpose experimental investigations were carried out to acquire the fundamental force displacement behavior of the shape memory membrane to design the optimal shape of the leaf spring element. The forces required to deform the shape memory membrane in the martensitic and austenitic state were measured with respect to the membranes displacement using a load cell and a linear variable differential transformer. The displacements of the membrane were introduced using a linear bearing system. The calculations for the design of an optimal leaf spring and especially its initial shape were carried out using a discrete multi body system consisting of beam elements and torsional springs. The leaf spring with the calculated optimal shape was fabricated and incorporated into the system. The displacement behavior of the system during heating and cooling was measured using an optical distance sensor. For the analyzed temperature range up to 100 °C, the paper describes the methodological appropriacy and relevance towards the application domain for evaluated temperatures.

Commentary by Dr. Valentin Fuster
2013;():V002T02A002. doi:10.1115/SMASIS2013-3084.

Capsule-type micro actuator driven by the volume change of hydrogen storage alloys (HSA-CMA) was proposed to be applied as an actuator mounted on the joints of the super multilink manipulator to capture space debris. This actuator consists of a hollow sphere frame made of aluminum, a membrane of hydrogen storage alloys and a valve, and is compact and lightweight. The aim of this study was to evaluate the availability of HSA-CMA. Finite element analyses were performed to investigate the actuator displacement and the generating force as the static performance, and the obtained static performances were compared with that of other smart actuators. The analysis on the actuator displacement led to the design map of HSA-CMA. The comparison result suggests that HSA-CMA has the actuator displacement and the generating force as well or better than other smart actuators and that it is suitable for use in space.

Commentary by Dr. Valentin Fuster
2013;():V002T02A003. doi:10.1115/SMASIS2013-3089.

This article presents the development of a 2D model for HTSMA which focus on interfaces motion in the martensitic state. We consider the topology of a 2D representative “volume” constituted of 4 martensite variants. Interfacial force is derived using Eshelby’s energy momentum tensor ans compared with a critical threshold which depends on interfacial lenght. A criterion for annihiling compatible interfaces is incorporated in this framework. The model is firtly applied to the description of detwinning mechanism in a grain. First results are presented.

Commentary by Dr. Valentin Fuster
2013;():V002T02A004. doi:10.1115/SMASIS2013-3093.

Many three-dimensional constitutive models have been proposed to enhance the analysis and design of shape memory alloy (SMA) structural components. Phenomenological models are desirable for this purpose since they describe macroscopic responses using internal variables to govern the homogenized material response. Because they are computationally efficient on the scale of millimeters to meters, these models are often the only viable option when assessing the response of full-scale SMA components for engineering applications. Thus, many different 3D SMA constitutive models have been developed. However, for their intended user, the application engineer, a clear and straightforward methodology has not been established for selecting a model to use in a design process. A primary goal of the Consortium for the Advancement of Shape Memory Alloy Research and Technology (CASMART) modeling working group has been establishment of model selection methodology. One critical step in this process is the development of benchmark problems that clearly illustrate the capabilities and efficiencies of models. In this paper, we propose a set of benchmark problems centered on an SMA tube component. These problems have been selected to demonstrate both uniaxial and multiaxial, actuation and superelastic capabilities of 3D SMA models. We then use finite element simulations of these benchmark problems to compare and contrast both the material modeling and implementation of three unique SMA constitutive models.

Commentary by Dr. Valentin Fuster
2013;():V002T02A005. doi:10.1115/SMASIS2013-3100.

Airframe noise is a significant part of the overall noise produced by typical, transport-class aircraft during the approach and landing phases of flight. Leading-edge slat noise is a prominent source of airframe noise. The concept of a slat-cove filler was proposed in previous work as an effective means of mitigating slat noise.

Bench-top models were developed at 75% scale to study the feasibility of producing a functioning slat-cove filler. Initial results from several concepts led to a more-focused effort investigating a deformable structure based upon pseudoelastic SMA materials. The structure stows in the cavity between the slat and main wing during cruise and deploys simultaneously with the slat to guide the aerodynamic flow suitably for low noise.

A qualitative parametric study of SMA-enabled, slat-cove filler designs was performed on the bench-top. Computational models were developed and analyses were performed to assess the displacement response under representative aerodynamic load. The bench-top and computational results provide significant insight into design trades and an optimal design.

Commentary by Dr. Valentin Fuster
2013;():V002T02A006. doi:10.1115/SMASIS2013-3104.

Airframe noise is a significant component of environmental noise in the vicinity of airports. The noise associated with the leading-edge slat of typical transport aircraft is a prominent source of airframe noise. Previous work suggests that a slat-cove filler (SCF) may be an effective noise treatment. Hence, development and optimization of a practical slat-cove-filler structure is a priority. The objectives of this work are to optimize the design of a functioning SCF that incorporates superelastic shape memory alloy (SMA) materials as flexures that permit the deformations involved in the configuration change. The goal of the optimization is to minimize the actuation force needed to retract the slat-SCF assembly while satisfying constraints on the maximum SMA stress and on the SCF deflection under static aerodynamic pressure loads, while also satisfying the condition that the SCF self-deploy during slat extension. A finite element analysis model based on a physical bench-top model is created in Abaqus such that automated iterative analysis of the design could be performed. In order to achieve an optimized design, several design variables associated with the current SCF configuration are considered, such as the thicknesses of SMA flexures and the dimensions of various components, SMA and conventional. Design of experiment (DOE) studies are performed to investigate structural response to an aerodynamic pressure load and to slat retraction and deployment. DOE results are then used to inform the optimization process, which determines a design minimizing actuator forces while satisfying the required constraints.

Commentary by Dr. Valentin Fuster
2013;():V002T02A007. doi:10.1115/SMASIS2013-3105.

The main focus of this study is the optimization of a trilayer actuator comprising two layers of polypyrrole and a PVDF membrane core. Since the performance of these actuators is difficult to predict due to their mechanical and chemical properties, optimizing their output behavior such as the tip displacement and blocking force is of crucial importance for utilizing their full potentials and more significantly increasing predictability in their performance. For this purpose, two optimization techniques (multiobjective genetic algorithm and active set algorithm) have been carried out based on a developed mathematical model. Two nonlinear constrained equations representing the tip displacement and the blocking force are formulated and solved for a predetermined thickness of the PVDF core membrane. Both equations are subjected to a bound constraint and a nonlinear equality constraint. The output blocking force and the tip deformation act in a reverse manner and there is a trade-off between them. Accordingly, the results imply that there is no single solution to the problem and a range for each of the design variables should be determined so that there will be a sense of balance between the two objectives. Furthermore, the results obtained from the multiobjective optimization methodology have been verified experimentally.

Commentary by Dr. Valentin Fuster
2013;():V002T02A008. doi:10.1115/SMASIS2013-3142.

In this article we present the feasibility of using the shape memory alloy (SMA) wires, namely Nitinol, as an actuator for a steerable surgical cannula. A 3D finite element (FE) model of the actuated steerable cannula was then developed in ANSYS to show deflection of the surgical cannula under the actuation force. The behavior of SMAs was simulated by defining the isothermal stress-strain curves using the multi-elasticity capability of ANSYS. The transformation temperatures of the Nitinol wire at different levels of stress were gathered to form the transformation diagram. Using the one-dimensional Brinson model, the isothermal stress-strain response of the wire was obtained. The thermomechanical characteristics of SMAs were also studied completely by a series of experiments performed on the wires. Birth and death method was used in the solution procedure to have the prestrain condition on Nitinol wire prior to the actuation step. A prototype of the actuated steerable cannula was also developed to validate the numerical simulation. Finally a study was done on design parameters affecting the deflection such as Young’s modulus of cannula, SMA diameter and its offset from the neutral axis of the cannula which can be useful in design optimization.

Topics: Wire
Commentary by Dr. Valentin Fuster
2013;():V002T02A009. doi:10.1115/SMASIS2013-3143.

This work introduces the use of digital image correlation together with infrared thermography to study non-uniform deformations due localized heating of equiatomic NiTi. While this short paper focuses on demonstrating the mechanical response of the material to localized heating, future work will also demonstrate calibration and validation of a 3-D constitutive model of the material using the concepts presented here. A comparison is made between the behavior of the material due to localized heating and the behavior due to uniform heating and cooling. The relevant parameters used for calibration of the constitutive model are quantified using the results of an ambient heating and cooling experiment.

Commentary by Dr. Valentin Fuster
2013;():V002T02A010. doi:10.1115/SMASIS2013-3163.

Shape Memory Alloys (SMAs) have many promising applications in the aerospace, automotive, and energy industries. However, due to a lack of understanding of their actuation fatigue, applications are sometimes limited to non-structural or non-critical components. This paper addresses the actuation fatigue characteristics of a specific SMA, equiatomic Nickel-Titanium (NiTi), with varying heat treatments, as well as different methods for assessing actuation fatigue response, including improved testing procedures and distributed extension measurement methods. Heat treatments ranged from 350°C to 400°C for one to three hours. Dogbone specimens processed from heat treated NiTi sheets were mechanically loaded on test frames which provided resistive heating and forced convective cooling with dry air via vortex tubes. Two mechanical loading schemes were utilized: constant uniaxial load (initial stress of 200MPa) and a linear or spring load centered at 200MPa (and ranging from approximately 150MPa to 250MPa). Linear loading schemes were introduced in order to better simulate actuation in an aerospace application, such as the morphing of semi-rigid surfaces. Specimens were thermally cycled to full actuation with a time-based control scheme developed in LabVIEW. Fatigue responses varied widely as a result of different heat treatments and loading schemes. Due to the main failure mechanism being high localized extension (necking) for the constant loading schemes, additional hardware and software were developed to visually capture extension distribution over specimen length. By analyzing actuation characteristics (e.g. transformation strain) and fatigue mechanisms, the ideal post-processing for actuator applications was determined. Utilizing the local extension distribution evolution over the fatigue life of NiTi specimens as well as postmortem analysis of the failure surfaces allowed for the failure modes to be determined for each heat treatment.

Commentary by Dr. Valentin Fuster
2013;():V002T02A011. doi:10.1115/SMASIS2013-3167.

This paper presents the results of our fully coupled, two-dimensional (2D) simulation of the swelling behavior of glucose-sensitive hydrogels at a constant glucose level with change in the surrounding pH. The model consists of a system of glucose-sensitive hydrogel and ionic fluid as a solvent. The hydrogel consists of two enzymes: glucose-oxidase and catalase, which are immobilized on the polymeric network. The surrounding solvent has certain level of glucose. The diffusion of glucose from a solvent and its reaction within the hydrogel are simulated using the Nernst-Planck equation. The local electrical charge is calculated by the Poisson’s equation, and deformation of the hydrogel is determined by the mechanical field equation. These equations are fully coupled and simulations are performed for varying pH and glucose concentrations. The glucose concentration was taken at 7.7mM (140mg/mL) and the pH is varied from 6.8 to 7.4. As glucose reacts with oxygen, gluconic acid is produced in the presence of glucose-oxidase. The formation of gluconic acid within the gel results in protonation and thereby causes the hydrogel expansion. The glucose level in the surrounding solution limits diffusion in the hydrogel. As the surrounding solution pH increases the available fixed charged for ionization increases, which results in an increase in maximum equilibrium swelling and gluconic acid as a product of the reaction. The gluconic acid production was found to be proportional to the change in pH. The gluconic acid decreases the internal pH of the hydrogel, which ultimately reduced the deformation of the gel.

Commentary by Dr. Valentin Fuster
2013;():V002T02A012. doi:10.1115/SMASIS2013-3183.

The effect of precipitation on the thermo-mechanical properties of Ni-rich near-equiatomic NiTi Shape Memory Alloys (SMAs) is investigated via the finite element method. The thermo-mechanical response is simulated using a Representative Volume Element (RVE), which takes into account the structural effect of the precipitates, as well as the effect of the Ni-concentration gradient in the matrix. The Ni-distribution profile is evaluated using Fick’s law for diffusion. The obtained results reproduce several of the experimentally observed precipitation-induced changes on the transformation behavior characteristics of these materials.

Commentary by Dr. Valentin Fuster
2013;():V002T02A013. doi:10.1115/SMASIS2013-3184.

Higher order effects in ferroelectric materials are investigated by integrating electron density calculations using quantum mechanics into a homogenized, nonlinear continuum modeling framework. Electrostatic stresses based on the Hellmann-Feynman theorem are used to identify connections with the higher order quadrupole density. These higher order relations are integrated into a nonlinear mechanics free energy function to simulate electromechanical coupling. A specific example is investigated by conducting density functional theory (DFT) calculations on barium titanate and fitting the results to a thermodynamic potential function. Through the use of nonlinear geometric effects, electromechanical coupling is obtained without the use of electrostrictive or piezoelectric coupling coefficients.

Commentary by Dr. Valentin Fuster
2013;():V002T02A014. doi:10.1115/SMASIS2013-3187.

In this work, the effect of thermo-mechanically-induced global phase transformation (actuation) on the crack driving force in Shape Memory Alloys (SMAs) is investigated by means of the finite element method. The prototype problem of an infinite center-cracked SMA plate is analyzed during a thermal cycle in isobaric, plane strain loading conditions. The temperature variation is sufficient to induce global phase transformation. The Virtual Crack Closure Technique (VCCT) is employed to measure the crack tip energy release rate during the entire actuation cycle. Results show that the energy release rate can increase drastically during actuation, an order of magnitude for specific material systems. This in turn implies that crack growth may be triggered as a result of thermo-mechanically-induced phase transformation. The sensitivity of the crack tip energy release rate during actuation on key thermo-mechanical parameters is studied.

Commentary by Dr. Valentin Fuster
2013;():V002T02A015. doi:10.1115/SMASIS2013-3188.

Shape memory polymers (SMPs) are one of the most popular smart materials due to light weight and high elastic deformation capability. In this study, highly conductive carbon nanofibers paper (CNFP) was coated on the surface of SMP as a conductive layer for electro actuation of SMP. To overcome the drawback of low modulus and low strength of shape memory polymer (SMP), continuous carbon fiber reinforcement was also incorporated with SMP by autoclave processing. The dynamic mechanical analysis (DMA) result showed over 600% increase of storage modulus of SMP by introducing carbon fiber reinforcement. Also, the shape recovery time of SMP has been reduced over 150%, while the recovery ratio of SMP has been improved to 99% by incorporating with carbon fiber reinforcement. Additionally, the mechanical property degradation of SMP composites has been investigated after different electro actuation cycles. After 50 actuation cycles, the decrease of flexural modulus of SMP composites is negligible (< 2%), and the ultimate flexural strength of SMP composites only decreased 25%. The SMP composite shows high strength and modulus, and good durability.

Commentary by Dr. Valentin Fuster
2013;():V002T02A016. doi:10.1115/SMASIS2013-3200.

Shape Memory Alloy (SMA) composites are being increasingly investigated to address a variety of engineering problems. An application of growing interest is an SMA-MAX phase ceramic composite for use in extreme environments. By joining these two constituents, it is intended that the martensitic transformation of the SMA phase may be used with the unique kinking behavior of the MAX phases to improve the composite response. One particular intended outcome of this utilization is the development of residual stress states in the composite. These residual stress states are generated due to the formation of irrecoverable strains resulting from the interaction of the inelastic mechanisms in the system. By tailoring this stress state, the improved mechanical response of the ceramic phase under compression may be taken advantage of. These residual stress states and their effect on the effective thermomechanical response of the composite are explored in this work. To this end, a finite element model of the composite is development. Specifically, a recent 3D phenomenological constitutive model of the SMA phase is incorporated to describe the effects of martensitic transformation and a constitutive assumption for the MAX phase response associated with kink band formation is introduced. An additional non-transforming NiTi phase is noted and the role of its constitutive response is considered. This model is used to study the micromechanics of the associated composite residual stress states. The influence of these residual stresses on the effective actuation response is then investigated and the on the associated composite behavior determined. Specifically, it is shown that the variation in inactive NiTi leads to an altered actuation response.

Commentary by Dr. Valentin Fuster
2013;():V002T02A017. doi:10.1115/SMASIS2013-3211.

We present our simulation results of swelling responses of the pH-sensitive, 3D-arbitarary-geometry hydrogel in steady state conditions. The swelling responses of the hydrogels to the changes in environmental stimuli such as solution pH are discussed. The finite element simulation uses three nonlinear partial-differential equations for responsible physical phenomena namely- chemical for ionic transport across the hydrogel, electrical for local electric charge balance within hydrogel, and mechanical for expansion of the hydrogel by the Nernst-Planck, the Poisson’s, and the mechanical field equations respectively. In the case of pH-sensitive hydrogel, material properties such as modulus of elasticity and Poisson’s ratio changes with a change in surrounding environments. Finite element analysis used for present study was carried out by full coupling of above three partial-differential equations with variable material properties. Employing a moving mesh method for 3D geometry, the FEM simulation was performed to account for large-swelling of the pH-sensitive hydrogel. This highly nonlinear and computationally intensive simulation was performed using multicore parallel-processing computer. The simulation results using above mentioned strategy has been validated for 2D geometry and results are in agreement with other published experimental results.

Topics: Geometry , Hydrogels
Commentary by Dr. Valentin Fuster
2013;():V002T02A018. doi:10.1115/SMASIS2013-3223.

The formation/disruption of the electron hopping pathways is considered to be one of the dominant mechanisms affecting macroscale effective piezoresistive response of carbon nanotube (CNT)-polymer nanocomposites. In this study, a computational micromechanics model is developed using finite element techniques to capture the effect of electron hopping induced conductive pathways at the nanoscale which contribute to the macroscale piezoresistive response of the CNT-polymer nanocomposites. In addition, damage is allowed to evolve at the CNT-polymer interface through electromechanical cohesive zones resulting in disruption of electron hopping pathways in the direction of applied strain. The impact of the electron hopping mechanism and nanoscale interfacial damage evolution on the effective piezoresistive response is studied through the macroscale effective material properties and gauge factors evaluated using micromechanics techniques based on electrostatic energy equivalence. It is observed that the interfacial damage at the nanoscale results in lower gauge factors as compared to the perfectly bonded interface.

Commentary by Dr. Valentin Fuster
2013;():V002T02A019. doi:10.1115/SMASIS2013-3243.

Actuators based on dielectric electroactive polymers (DEAP) use the electrostatic pressure to convert electric energy into strain energy. Besides this, they are also predestined for sensor applications to monitor the actual stretch state based on the deformation dependent capacitive-resistive behavior of the DEAP. Considering DEAP actuators for positioning applications, like stack- or roll-actuators, the actual position, length or stretch of the actuator is required for a precise control. Thus, integrated sensors made of DEAP can be used to determine the actual stretch state with sufficient accuracy and high dynamics on the one hand. On the other hand the electrical behavior of the DEAP transducer itself can be evaluated for the estimation of the stretch state representing a sensor-less concept. In this paper at first the state of the art of sensor-based and sensor-less concepts for determining the stretch state of DEAP transducers is presented. Afterwards the authors propose novel concepts for DEAP-based sensors integrated into stack- and roll-actuators. These concepts are compared with each other in terms of sensitivity, accuracy, dynamics and integration efforts for the realization. Finally, fundamental concepts, estimation algorithms and different approaches for monitoring the actual stretch state are presented based on the electrical parameters of a lossy DEAP transducer, which are suitable both for sensor-based and sensor-less concepts.

Commentary by Dr. Valentin Fuster
2013;():V002T02A020. doi:10.1115/SMASIS2013-3259.

In this work a high-frequency dynamic model of a pre-loaded circular DEAP actuator is developed and experimentally validated. The model is capable of predicting both the static and dynamic response of the actuator. The static response is modeled based on a free energy approach and consists of an Ogden term representing the elastic energy, and a electrical term representing the electrical-mechanical coupling [1]. The addition of viscoelastic elements (spring-dashpot configurations) enables the model to capture the dynamic response. The Ogden coefficients were first identified through a quasi-static force-displacement test of the actuator. A series of validation tests of the actuator at various pre-loads and voltage frequencies showed the model to be in good agreement with the experiments. The model is shown to accurately predict the actuators observed natural frequencies as the pre-deflection and the stiffness of the spring were changed. Future work will include additions to the model to account for relaxation and creep inherent in DEAP material.

Commentary by Dr. Valentin Fuster
2013;():V002T02A021. doi:10.1115/SMASIS2013-3279.

Relaxor ferroelectric single crystals such as PMN-PT and PIN-PMN-PT undergo field driven phase transformations when electrically or mechanically loaded in crystallographic directions that provide a positive driving force for the transformation. The observed behavior in certain compositions is a phase transformation distributed over a range of field levels without a distinct forward or reverse coercive field. This work focuses on the material behavior that is observed when the crystals are loaded sufficiently to drive a partial transformation and then unloaded as might occur when driving a transducer to achieve high power levels. A set of experiments was conducted to characterize the minor hysteresis loops that occur with the partial transformations. Distributed transformations have been modeled using a Gaussian distribution of transformation thresholds. In this work the Gaussian model is extended to include the partial transformations that occur when the field is reversed before the transformation is complete. The resulting minor hysteresis loops produced by the model are in good agreement with the experimental results.

Commentary by Dr. Valentin Fuster
2013;():V002T02A022. doi:10.1115/SMASIS2013-3303.

Piezoelectric materials exhibit electromechanical coupling which has led to their widespread application for sensors, actuators, and energy harvesters. These materials possess anisotropic behavior with the shear coefficient have the largest electromechanical coupling coefficient. However the shear mode is difficult to measure with existing techniques and thus has not been fully capitalized upon in recent devices. Better understanding of the full shear response with respect to the driving electric field would significantly help the design of optimized piezoelectric shear devices. Here a simple and low cost direct measurement method based on digital image correlation is developed to characterize the shear response of piezoelectric materials and its nonlinear behavior as a function of external field. The piezoelectric shear coefficient (d15) of a commercial shear plate actuator is investigated in both bipolar and unipolar electric fields. Two different nonlinearities and hysteresis behaviors of the actuators were observed, and the relation between the driving field amplitude and the corresponding d15 coefficient is determined. Moreover, the measured transverse displacement of the plate actuator in simple shear condition is validated through a laser interferometry technique.

Commentary by Dr. Valentin Fuster
2013;():V002T02A023. doi:10.1115/SMASIS2013-3325.

Dielectric electro-active polymers (DEAP) are an attractive material for use in actuator technologies due to their lightweight, high energy density, high energy efficiency, scalability and low noise features. In real world applications, DEAP actuators and sensors will be subjected to various environmental conditions such as changing temperatures. The effects of these environmental changes need to be understood in order to not only optimize performance, but also document environmental limitations and possibly protect against or compensate for them. This paper presents a systematic experimental investigation of the mechanical and electrical behavior of a silicone based DEAP actuator/sensor under varying controlled temperature conditions. Measurements are performed in a climactic chamber with controlled temperatures from −10 to +60 °C. During these tests, a particular focus was placed on the mechanical hysteresis and viscoelastic effects for actuator performance and on the changes in capacitance for sensor performance. For various constant temperatures, the DEAP was subjected to out of plane displacement loading, while the force and capacitance was measured. The effects of the viscous component of the viscoelastic DEAP material is shown to decrease with increased temperature. The capacitance of the DEAP is also shown to decrease with increased temperature. These results will effect actuator and sensor performance respectively and will be used for DEAP application design considerations and improve future modeling efforts.

Commentary by Dr. Valentin Fuster
2013;():V002T02A024. doi:10.1115/SMASIS2013-3337.

Shape memory alloy (SMA) actuator wires promise substantial size, weight, and potential cost advantages over their solenoid and electric motor counterparts. Designing actuators which fully realize these advantages is hampered by a limited understanding of how interactions between wires and their environment affect cyclic lifetime. For example, many devices use two SMA wires mechanically in parallel but electrically in series. This has practical advantages in simplified electrical routing and thermal lag. However, it complicates modeling in that wires interact both electrically and mechanically.

Here we study the effect of a mismatch in length between two SMA wires in parallel. We perform a series of fatigue experiments to show that mismatch of up to 0.75%, at the chosen set of conditions, has no measurable effect on cycle life. We also perform a series of simulations to show how the mechanical interaction between the two parallel wires tends to suppress, rather than amplify, any impact of length mismatch.

Commentary by Dr. Valentin Fuster

Structural Health Monitoring

2013;():V002T05A001. doi:10.1115/SMASIS2013-3008.

One of the important issues to conduct the damage detection of a structure using vibration-based damage detection (VBDD) is not only to detect the damage but also to locate and quantify the damage. In this paper a systematic way of damage assessment, including identification of damage location and damage quantification, is proposed by using output-only measurement. Four level of damage identification algorithms are proposed. First, to identify the damage occurrence, null-space and subspace damage index are used. The eigenvalue difference ratio is also discussed for detecting the damage. Second, to locate the damage, the change of mode shape slope ratio and the prediction error from response using singular spectrum analysis are used. Finally, to quantify the damage the RSSI-COV algorithm is used to identify the change of dynamic characteristics together with the model updating technique, the loss of stiffness can be identified. Experimental data collected from the bridge foundation scouring in hydraulic lab was used to demonstrate the applicability of the proposed methods. The computation efficiency of each method is also discussed so as to accommodate the online damage detection.

Commentary by Dr. Valentin Fuster
2013;():V002T05A002. doi:10.1115/SMASIS2013-3009.

This paper presents a novel data-driven approach for detecting broken reciprocating compressor valves that is based on the idea that a broken valve will affect the shape of the pressure-volume (pV) diagram. This effect can be observed when the valves are closed. To avoid disturbances due to the load control we concentrate on the expansion phase linearized using the logarithmic pV diagram. The gradient of the expansion phase serves as an indicator of the fault state of the valves. Since the gradient is also affected by the pressure conditions, they are used as an additional indicator. After feature extraction and removing offset in the feature space by solving an optimization problem, classification of different valve types can be achieved with one support vector machine classifer. The performance of the method was validated by analyzing real-world measurement data. Our results show a very high classification accuracy for varying compressor load and pressure conditions.

Commentary by Dr. Valentin Fuster
2013;():V002T05A003. doi:10.1115/SMASIS2013-3010.

To localize small damage from mode shapes, the polynomial annihilation edge detection method has been proposed and demonstrated its effectiveness on different types of structural components [7]. However, much computational effort involved in this approach lowers the damage detection speed. To alleviate this difficulty, in this paper, we improve the approach by first using the divided difference approach to identify the region(s) in which jump discontinuities are located, and then only applying the polynomial annihilation method to points in the identified region. In this way, the computational burden of this approach is significantly relieved, while the accuracy is still maintained. The improved approach has been validated by numerical simulations on a cable-stayed bridge model. This approach only requires post-damage mode shapes.

Topics: Edge detection
Commentary by Dr. Valentin Fuster
2013;():V002T05A004. doi:10.1115/SMASIS2013-3022.

In this study, a new damage detection algorithm for specific types of damages such as breathing cracks, which are called “active discontinuities” in this paper, is proposed. The algorithm is based on the nonlinear behavior of this class of damages and hence, is more precise and sensitive to damage compared to other common linear methods. The active discontinuities can be regarded as additional degrees of freedom (DOFs) which need energy to be excited. Because the input energy of both the intact and the damaged structures is finite, the energy content of vibrating modes will be changed due to damage. Thus, the properties of distribution of energy between vibrating modes can be used as indices for detecting damage. An essential detectability condition using this concept is decomposing a signal such that no spurious mode imposed to its expansion. In order to satisfy this condition, Empirical Mode decomposition (EMD) is used to extract the vibrating modes since all nonlinearities in a signal are preserved while no spurious mode or assumption of stationarity is imposed on the problem. Prevention of mode mixing, which is an important drawback of EMD, is another necessary condition for robustness of the algorithm. A solution is proposed in this paper to satisfy this condition in which special constraints are imposed on the normal procedure of EMD. Then, the fourth central moment, kurtosis, is used to compare the distribution of energy between the modified vibrating modes. The algorithm is verified through experimental testing of a simple steel cantilever structure under various damage scenarios. Results demonstrate the efficacy of the method for detecting discontinuities in a real structure.

Commentary by Dr. Valentin Fuster
2013;():V002T05A005. doi:10.1115/SMASIS2013-3024.

In this study, a guided wave phased array beamsteering approach is applied to composite laminates. Current beamsteering algorithms derived for isotropic materials assume omnidirectional wave propagation. Due to inherent anisotropy in composites, guided wave propagation varies with direction and wavefronts no longer have perfect circular shapes.

By examining slowness, velocity and wave curves for a given composite laminate, the wavefront from a single source can be described as a function of the angle of propagation and distance from origin. Using this approach, a generic delay and sum beamforming algorithm for composite laminates is developed for any desired wave mode.

It is shown that anisotropic wave mode regions can be effectively used for beamsteering in certain directions with a linear array and performance similar or even better than isotropic case. However, the useful range of angles with a 1d linear array for anisotropic wave modes is quite small and other directions exhibit undesired grating lobes and large sidelobes.

Commentary by Dr. Valentin Fuster
2013;():V002T05A006. doi:10.1115/SMASIS2013-3087.

Optical fiber temperature sensing systems have incomparable advantages than the traditional electric cable based monitoring systems. As of now, fiber Bragg grating (FBG) sensors are most popular because of its wavelength domain multiplexing capability. However, grating writing process is complex and takes long time and photosensitive fibers for the typical grating writing process are expensive. In addition, sensing systems for FBGs are also expensive. Therefore, this study proposes multiplexed fiber optic temperature monitoring sensor system using an economical Optical Time-Domain Reflectometer (OTDR) and Hard-Polymer-Clad Fiber (HPCF). HPCF is a specific type of optical fiber, in which a hard polymer cladding made of fluoroacrylate acts as a protective coating for an inner silica core. An OTDR is an optical loss measurement system that provides optical loss and event distance measurement in real time. Multiplexed sensor nodes were economically and quickly made by locally stripping HPCF clad through photo-thermal and photo-chemical processes using a continuous/pulse hybrid-mode laser with 10 m intervals. The core length exposed was easily controlled by adjusting the laser beam diameter, and the exposed core created a backscattering signal in the OTDR attenuation trace. The backscattering peak was sensitive to the temperature variation. Since the elaborated HPCF temperature sensor was insensitive to strain applied to the sensor node and to temperature variation in the normal HPCF line, neither strain compensation nor isolation technique are required. These characteristics are important advantages for the use as structure-integrated temperature sensors. The performance characteristics of the sensor nodes include an operating range of up to 120 C, a resolution of 1.52 C, a tensile strain resistance of 13%.

Commentary by Dr. Valentin Fuster
2013;():V002T05A007. doi:10.1115/SMASIS2013-3088.

Interest in ultrasonic guided wave based Structural Health Monitoring and a nondestructive evaluation system has grown in recent years, especially to monitor thin plate like structures. However, an effective signal processing and imaging algorithms are essential to achieve necessary performance. This paper describes wave rich laser ultrasonic wavenumber imaging method (UWI) method for damage visualization. Ultrasonic waves were generated by a scanning laser source and acquired using a capacitance air coupled transducer (ACT). However, the inherent existence of multiple Lamb wave modes in signal makes it harder for effective damage evaluation. This is further complicated if the reflections from the boundaries are present in the signal. The use of an ACT with an in-line programmable filter helps to isolate lower order Lamb wave modes (Ao and So), since the dispersive waves radiate at certain angle from the specimen governed by Snell’s law. By comparing the results from the ultrasonic wavefield image obtained using the ACT and a PZT contact sensor under the same experimental condition, mode isolation phenomena was verified.

Such isolated wave mode was processed using a proposed wave rich UWI algorithm where a wave rich field was generated by superposing the wavefields. The mode filtered measurements were arranged in 3D space-time domain where each slice in time domain represents 2D wavefield image. A 2D Fast Fourier Transform (FFT) was applied to this spatial information in time domain which transformed it to a wavenumber domain. A wavenumber filter is then applied and inverse Fourier transformed to get back to the wavenumber filtered measurement. However, instead of applying filter to every 2D slice in time domain, certain frames were selected and merged to replicate wave propagation in total scan-area. This wave rich field not only saves time and space but also reduce computational complexity during post-processing. This method was tested successfully in an aluminum plate with milled area damage and a composite fiber-reinforced plastic (CFRP) wing skin with two impact damages.

Commentary by Dr. Valentin Fuster
2013;():V002T05A008. doi:10.1115/SMASIS2013-3107.

Embedded smart actuators/sensors, such as piezoelectric types, have been used to conduct wave transmission and reception, pulse-echo, pitch-catch, and phased array functions in order to achieve in-situ nondestructive evaluation for different structures. By comparing to baseline signatures, the damage location, amount, and type can be determined. Typically, this methodology does not require analytical structural models and interrogation algorithm is carefully designed with little wave propagation knowledge of the structure. However, the wave excitation frequency, waveform, and other signal characteristics must be comprehensively considered to effectively conduct diagnosis of incipient forms of damage. Accurate prediction of high frequency wave response requires a prohibitively large number of conventional finite elements in the structural model. A new high fidelity approach is needed to capture high frequency wave propagations in a structure.

In this paper, a spectral finite element method (SFEM) is proposed to characterize wave propagations in a beam structure under piezoelectric material (i.e., PZT) actuation/sensing. Mathematical models are developed to account for both Uni-morph and bi-morph configurations, in which PZT layers are modeled as either an actuator or a sensor. The Timoshenko beam theory is adopted to accommodate high frequency wave propagations, i.e., 20–200 KHz. The PZT layer is modeled as a Timoshenko beam as well. Corresponding displacement compatibility conditions are applied at interfaces. Finally, a set of fully coupled governing equations and associated boundary conditions are obtained when applying the Hamilton’s principle. These electro-mechanical coupled equations are solved in the frequency domain. Then, analytical solutions are used to formulate the spectral finite element model. Very few spectral finite elements are required to accurately capture the wave propagation in the beam because the shape functions are duplicated from exact solutions. Both symmetric and antisymmetric mode of lamb waves can be generated using bimorph or uni-morph actuation. Comprehensive simulations are conducted to determine the beam wave propagation responses. It is shown that the PZT sensor can pick up the reflected waves from beam boundaries and damages. Parametric studies are conducted as well to determine the optimal actuation frequency and sensor sensitivity. Such information helps us to fundamentally understand wave propagations in a beam structure under PZT actuation and sensing. Our SFEM predictions are validated by the results in the literature.

Commentary by Dr. Valentin Fuster
2013;():V002T05A009. doi:10.1115/SMASIS2013-3135.

This paper examines the performance of fiber Bragg gratings (FBGs) as embedded heat flux sensors for ablative thermal protection systems (TPS). Ablative TPS materials are currently used for reentry spacecraft applications because ablative TPS materials are able to withstand the higher temperatures present in ballistic reentry than non-ablative materials. It is important to measure the through-the-thickness temperature profile in-situ to verify the heat shielding performance. FBG sensors were chosen to monitor the temperature in the TPS primarily because of a good match in the thermal properties of the silica fibers and the TPS material. A TPS specimen was subjected to a conductive and steady thermal load. Two FBG sensor arrays were embedded in the TPS specimen. One array was embedded horizontally in the specimen near the surface where the heat was applied, and the second array was embedded diagonally through the thickness of the specimen. The temperature load was produced using the lower platen of a hot press, and the maximum temperature was below the ablation temperature of the material. After the specimen was heated, it was removed from the hot press and allowed to passively cool on a metal table. The peak wavelength output from each sensor was monitored and recorded during the loading cycle, and the wavelength measurements were converted to temperature data over time. The test was completed three times, and excellent repeatability was present across the three tests and the temperature response of the FBGs was reasonable, even though the test setup was torn down and reassembled between two of the tests. Thermal images of the specimen were also collected during the test with an IR camera. The thermal images were used to provide a temperature map of the specimen which showed good agreement with the FBG data.

Commentary by Dr. Valentin Fuster
2013;():V002T05A010. doi:10.1115/SMASIS2013-3164.

For the past decade, wind turbines have become the largest source of installed renewable-energy capacity in the United States. Economical, maintenance and operation are critical issues when dealing with such large slender structures, particularly when these structures are sited remotely. Because of the chaotic nature of non-stationary rotating-machinery systems such as the horizontal-axis wind turbines (HAWTs), in-operation modeling and computer-aided numerical characterization is typically troublesome, and tends to be imprecise while predicting the real content of the actual aerodynamic loading. Loading environment under operation conditions is usually substantially different from those driven by modal testing or computer-aided model characterization and difficult to measure directly in the field. In addition, rotational machinery such as HAWTs exhibit complex and nonlinear dynamics (i.e., precession and Coriolis effects, torsional coupling, nonlinear geometries, plasticity of composite materials); and are subjected to nonlinear constrained conditions (i.e., aeroelastic interaction). For those reasons, modal-aeroelastic and computer-aided models reproduced under controlled conditions may fail to predict the correct non-stationary loading and resistance patterns of wind turbines in actual operation. Operational techniques for extracting modal properties under actual non-stationary loadings are needed in order to (1) improve computer-aided elasto-aerodynamic models to better characterize the actual behavior of HAWTs in operational scenarios, (2) improve and correlate models, (3) monitor and diagnose the system for integrity and damage through time, or even (4) optimize control systems. For structural health monitoring (SHM) applications, model updating of stochastic aerodynamic problems has gained interest over the past decades. For situations where optimizing objective functions are not differentiable, convex or continuous in nature that is the case of gradient methods such as Modal Assurance Criterion (MAC), global optimization (metaheurstic) methods based on probability principles have emerged. These search engine techniques are promising suitable to cope with non-stationary-stochastic system identification methods for model updating of HAWT systems. A probability theory framework is employed in this study to update the wind turbine model using such a stochastic global optimization approach. Structural identification is addressed under regular wind turbine operation conditions for non-stationary, unmeasured, and uncontrolled excitations by means of the eigensystem realization theory (ERA). This numerical framework is then tied up with an adaptive simulated annealing (ASA) numerical engine for solving the problem of model updating. Numerical results are presented for an experimental deployment of a small HAWT structure. Results are benchmarked and validated with other empirical mode-decomposition and time-domain solutions.

Commentary by Dr. Valentin Fuster
2013;():V002T05A011. doi:10.1115/SMASIS2013-3173.

The usage of ultrasonic guided Lamb wave approach in structural health monitoring has been prevalent and proven to be an effective method. During flight, aircraft or spacecraft structures sometimes experience rapid temperature changes. The propagation of guided Lamb waves can be affected by these abrupt changes. In this paper, the effects of rapid temperature variation, due to which a sharp temperature gradient is achieved, on the propagation of guided Lamb waves through aluminum and composite beams are compared. The heating and cooling cycles for gradual temperature changes are firstly obtained for comparison. An abrupt change in the temperature is brought out by heating the beam to an elevated temperature and rapidly cooling it using liquid nitrogen. The design guidelines for the experimental setup used in the research are provided. The effects of rapid change in the temperature on the piezoelectric wafer active sensors (PWAS) are measured. Two different adhesives between the PWAS sensors and the beams are tested and the results obtained from the experiments are discussed.

Commentary by Dr. Valentin Fuster
2013;():V002T05A012. doi:10.1115/SMASIS2013-3265.

The objective of this study was to determine the deflected wing shape and the out-of-plane loads of a large-scale carbon-composite wing of an ultralight aerial vehicle using Fiber Bragg Grating (FBG) technology. The composite wing, subjected to concentrated and distributed loads, was instrumented with an optical fiber on its top and bottom surfaces positioned over the main spar, resulting in approximately 780 strain sensors bonded to the wings. The in-plane strains from the FBG sensors were used to obtain the out-of-plane loads as well as the wing shape at various load levels using NASA-developed real-time load and displacement algorithms. The calculated out-of-plane displacements and loads were generally within 4% of the measured data.

Commentary by Dr. Valentin Fuster
2013;():V002T05A013. doi:10.1115/SMASIS2013-3269.

As the field of Structural Health Monitoring (SHM) expands to spacecraft applications, the understanding of environmental effects on various SHM techniques becomes paramount. In January of 2013, an SHM payload produced by New Mexico Tech was sent on a high altitude balloon flight to a full altitude of 102,000 ft. The payload contained various SHM experiments including impedance measurements, passive detection (acoustic emission), active interrogation (guided waves), and wireless strain/temperature sensing. The focus of this paper is the effect of altitude on the active SHM experiments. The active experiment utilized a commercial SHM product for generation and reception of elastic waves that enabled wavespeed measurements, loose bolt detection, and crack detection through the full profile of the flight. Definite deviations were observed in the data through the stages of the flight which included a ground, ascent, float, and descent phases. Several elements of the high altitude environment can have an effect on the measurement such as temperature and pressure. The flight data was compared against a ground altitude baseline and heavy emphasis is placed on comparing changes in the data with the temperature profile of the flight. Conclusions are drawn on the effect of altitude on wavespeed of elastic waves, crack detection, and the sensing of a loose bolt.

Commentary by Dr. Valentin Fuster
2013;():V002T05A014. doi:10.1115/SMASIS2013-3287.

Filament wound composite pressure vessel with thin-wall alloy liner might exist local buckling during manufacture and in service, this phenomenon have great influence on the security and service lifetime of pressure vessel. AE (acoustic emission) technique is employed to monitor the damage progression of the vessel during hydraulic pressure experiment. Two sensors of acoustic emission (AE) were attached to front dome and cylinder to monitoring the behavior of the vessel bearing maximum 4.5MPa water pressure during loading, keeping load and unloading. Meanwhile ten strain gauges were bonded to front dome, equator and cylinder of the outer surface by meridian and hoop direction respectively in order to monitor the vessel deformation characters. Analysis show that strain gauges is suitable for evaluate deformation character of the outer surface of the vessel. Analysis indicated AE is more suitable to monitoring the damage propagation of the vessel. AE analysis explained the local buckling of inner thin-wall liner.

Commentary by Dr. Valentin Fuster
2013;():V002T05A015. doi:10.1115/SMASIS2013-3288.

Guided ultrasonic waves (GUW) have the potential to be an efficient and cost-effective method for rapid damage detection and quantification of large structures. Attractive features include sensitivity to a variety of damage types and the capability of traveling relatively long distances. They have proven to be an efficient approach for crack detection and localization in isotropic materials. However, techniques must be pushed beyond isotropic materials in order to be valid for composite aircraft components.

This paper presents our study on GUW propagation and interaction with delamination damage in composite structures using wavenumber array data processing, together with advanced wave propagation simulations. Parallel elastodynamic finite integration technique (EFIT) is used for the example simulations. Multi-dimensional Fourier transform is used to convert time-space wavefield data into frequency-wavenumber domain. Wave propagation in the wavenumber-frequency domain shows clear distinction among the guided wave modes that are present. This allows for extracting a guided wave mode through filtering and reconstruction techniques. Presence of delamination causes spectral change accordingly. Results from 3D CFRP guided wave simulations with delamination damage in flat-plate specimens are used for wave interaction with structural defect study.

Commentary by Dr. Valentin Fuster
2013;():V002T05A016. doi:10.1115/SMASIS2013-3290.

The paper presents a structural health monitoring method that is based on the model updating method connectivity constrained reference basis. The method combines two separate approaches, reference basis and parametric methods, and it is computationally efficient because it does not require calculation of sensitivity functions. The paper discusses why connectivity constrained reference basis is generally suitable for structural health monitoring and what are the modifications required in the new application. The derivation includes noise propagation analysis of the algorithm and its effect on the new structural health monitoring application.

Commentary by Dr. Valentin Fuster
2013;():V002T05A017. doi:10.1115/SMASIS2013-3317.

In the United States, many civil, aerospace, and military aircraft are nearing the end of their service life. Many of these service life predictions were determined by models that were created at the time of the design of the structure, possibly decades ago. As a precaution, these structures are inspected on a regular basis with techniques that tend to be expensive and laborious, such as tear-down inspections of aircraft. To complicate matters, new complex materials have been incorporated in recent structures to take advantage of their desirable properties, but these materials sustain damage in a manner that is different from that of past monolithic materials. One example is fiber-reinforced polymer (FRP) composites, which are heterogeneous, direction-dependent, and tend to manifest damage internal to their laminate structure, thus making the detection of this damage nearly impossible. For these reasons, numerous groups have focused on developing sensors that can be applied to or embedded within these structures to detect this damage. Some of the most promising of these approaches include using piezoelectric materials as passive or active ultrasonic sensors and actuators, fiber optic-based sensors to measure strain and detect cracking, and carbon nanotube-based sensors that can detect strain and cracking. These are mostly point-based sensors that are accurate at the location of application but require interpolative methods to ascertain the structural health elsewhere on the structure. To conduct direct damage detection across a structure, we have coupled the ability to deposit a carbon nanotube thin film across large substrates with a spatially distributed electrical conductivity measurement methodology called electrical impedance tomography. As indicated by previous research on carbon nanotube thin films, the electrical conductivity of these films changes when subjected to strain or become damaged. Our structural health monitoring strategy involves monitoring for changes in electrical conductivity across an applied CNT thin film, which would indicate damage. In this work, we demonstrate the ability of the Electrical Impedance Tomography (EIT) methodology to detect, locate, size, and determine severity of damage from impact events subjected to glass fiber-reinforced polymer composites. This will demonstrate the value and effectiveness of this next-generation structural health monitoring approach.

Commentary by Dr. Valentin Fuster

Bioinspired Smart Materials and Systems

2013;():V002T06A001. doi:10.1115/SMASIS2013-3017.

This paper describes the development of a tube-shaped ionic polymer-metal composite (IPMC) actuator with sectored electrodes and an integrated resistive strain-based displacement sensor. Tube or cylindrical shaped IPMC actuators, with the ability to provide multiple degrees-of-freedom motion, can be used to create active catheter biomedical devices and novel bio-inspired propulsion mechanisms for underwater autonomous systems. An experimental tube-shaped IPMC actuator is manufactured from a 40-mm long Nafion polymer tube with inner diameter of 1.3 mm and outer diameter of 1.6 mm. The outer surface of the tube-shaped structure is plated with platinum metal via an electroless plating process. The platinum electrode on the tube’s outer surface is sectored into four isolated electrodes using a simple surface milling technique. A custom-designed strain sensor comprised of 50 AWG ni-chrome wire is developed and attached to the tube’s surface to sense the bending motion of the tube actuator. The integrated sensor is low cost and practical, and it avoids the need for bulky external sensors such as lasers for measuring deflection and feedback control. Preliminary experimental results are presented to demonstrate the performance of the IPMC tube actuator and integrated displacement sensor.

Commentary by Dr. Valentin Fuster
2013;():V002T06A002. doi:10.1115/SMASIS2013-3021.

The inner hair cells (IHC’s) and outer hair cells (OHC’s) in the cochlea are vital components in the process of hearing. The IHC’s are responsible for converting sound-induced vibration into electrical signals. The OHC’s produce forces that amplify these vibrations and therefore enhance the electrical signals produced by the IHC’s. The resulting “cochlear amplifier” produces a nonlinear amplification which gives the ear its ability to detect sound pressure levels ranging from 20 μPa to 20 Pa (0 to 120 dB).

This paper presents the modeling and testing of an artificial hair cell (AHC) piezoelectric sensor inspired by the hair cells found in the mammalian ear. The sensor is a bimorph cantilever beam consisting of a sensing piezoceramic element and an actuating piezoceramic element bonded to a brass substrate. The sensing element is used to detect the mechanical motion of the beam. Output feedback control can be used to send a voltage signal to the actuating element and alter the frequency response of the beam. A control law, which modifies the linear damping term of the first mode and introduces cubic damping, is used to create a closed-loop system perched at a Hopf bifurcation. The result is a system that produces a nonlinear amplification of the beam’s mechanical response in a manner which mimics the nonlinear behavior of the mammalian cochlea. This active sensor is studied under base acceleration and the initial test results are compared to a finite element model. Simulations of the closed-loop system are examined for the system with a single mode and for the system with multiple modes.

Commentary by Dr. Valentin Fuster
2013;():V002T06A003. doi:10.1115/SMASIS2013-3027.

In this research, a concept of earthworm-like robot with fluidic flexible matrix composite (F2MC) segments as its actuators is investigated. It explores a novel application of F2MC in the bionics field. Firstly, a general kinematics model of robot with earthworm-like locomotion is developed. Based on this model, the locomotion mechanism is analyzed in order to determine the actuation performance requirement for the F2MC segment. Then an analytical model of the F2MC segment is adopted to estimate the finite deformation under internal pressurization. By doing so, the optimal configuration of the F2MC segment that meets the requirements as an actuator is determined. A conceptual design of the earthworm-like robot based on F2MC segment is presented. After that, robotic gaits are constructed based on the kinematic locomotion mechanism with some necessary physical assumptions. Directed locomotion can be achieved based on the constructed gaits. Aiming at increasing the average velocity and motion efficiency of the robot, locomotion gaits are optimized. Optimal gaits corresponding to the maximal velocity and maximal locomotion efficiency are obtained, respectively.

Commentary by Dr. Valentin Fuster
2013;():V002T06A004. doi:10.1115/SMASIS2013-3031.

A contact aided compliant mechanism called twist compliant mechanism is presented in this paper. This mechanism has nonlinear stiffness when it is twisted in both directions along its axis. The inner core of the mechanism is responsible for its flexibility in one twisting direction. The contact surfaces of the cross-members and compliant sectors are responsible for its high stiffness in the opposite direction. A twist compliant mechanism with desired twist angle and stiffness can be designed by choosing the right thickness of its cross-members, thickness of the core and thickness of its sectors. A multi-objective optimization problem with three objective functions is proposed in this paper, and used to design an optimal twist compliant mechanism with desired deflection. The objective functions are to minimize the mass and maximum von Mises stress observed, while minimizing or maximizing the twist angles under specific loading conditions. The multi-objective optimization problem proposed in this paper is solved using an ornithopter flight research platform as a case study, with the goal of using the twist compliant mechanism to achieve passive twisting of the wing during upstroke, while keeping the wing fully extended and rigid during the downstroke. Prototype twist compliant mechanisms have been fabricated using a waterjet cutter and will be tested as part of future work.

Commentary by Dr. Valentin Fuster
2013;():V002T06A005. doi:10.1115/SMASIS2013-3044.

A knee-ankle-foot orthosis (KAFO) spans the knee, ankle and foot, and assists in the walking motion of those who suffer neuromuscular deficiencies. KAFOs can be classified as passive, semi-dynamic and dynamic. Passive KAFOs lock the knee joint during the whole gait cycle. Semi dynamic KAFOs lock the knee joint during the stance phase. Dynamic KAFOs attempt to reproduce normal knee motions during the whole gait cycle. Two types of dynamic KAFOs have been reported in the literature. The first one is activated by using a pneumatic system, and the second one uses a spring mechanism. Both systems are bulky and controlled through complex control systems that limit their application as assistive devices. The purpose of our research is to develop a dynamic KAFO that is actuated easily by employing shape memory materials. Such an actuation system makes the KAFO lightweight and with a great commercialization potential. The purpose of this paper is to present a conceptual design for the knee actuator of a dynamic KAFO. This actuator uses torsional shape memory rods to match the stiffness of the knee joint of the KAFO with that of a normal knee joint during the walking gait cycle. Joint stiffness is measured by the moment around the joint per degree of joint rotation. The proposed actuator includes two parts that work independently during the two phases of the gait cycle. The first part engages only during the stance phase and the other works only during the swing phase. Each part is developed by combining a superelastic (SE) rod and a rotary spring in series. The conceptual design is verified by simulation. The simulation results show that the proposed knee actuator reproduces the stiffness of the normal knee joint during the whole gait cycle. It is thus possible to develop a novel dynamic KAFO that can provide normal knee stiffness characteristics to assist individuals with quadriceps deficiency.

Topics: Actuators , Orthotics , Knee
Commentary by Dr. Valentin Fuster
2013;():V002T06A006. doi:10.1115/SMASIS2013-3068.

This paper focuses on developing a closed fluidic environment for packaging biomolecular unit cells, which consists of a synthetic lipid bilayer and other biomolecules contained in a near solid-state material with two regions that contain hydrophobic oil (i.e. nonpolar solvent) surrounding aqueous droplets. This research provides a stepping-stone towards an autonomic biomolecular material system, whereby a packaged system will allow for precise droplet interface bilayer (DIB) formation without the interference of outside contamination for long-term applications. Also, substrate materials need to maintain droplets and preserve the self-assembly and stimuli-responsive properties of biomolecules within the unit cell. A critical feature of an encapsulating material is that it does not absorb either of the liquid phases required to form DIBs. Oil depletion tests within sealed, polymeric substrates show that polydimethylsiloxane (PDMS) absorbs full volume of injected hexadecane in approximately 27 hours. However, polyurethane substrates maintain the original amount of oil injected even after several weeks. Bilayer lifetime is also monitored within an environment in which the oil is also depleting. The results of this test show the longevity of a DIB to be shorter than oil lifetime. The lipid-encased droplets disconnect after approximately 10 hours, when there is only approximately <60% amount of oil present. In addition, an initial microfluidic substrate is designed such that a single T-junction intersection can be used to form monodisperse droplets within a primary oil-filled channel and a downstream increase in channel width can be used to connect droplets to form DIBs.

Commentary by Dr. Valentin Fuster
2013;():V002T06A007. doi:10.1115/SMASIS2013-3075.

Bio-inspiration has introduced new and innovative flow control methods in gust alleviation, maneuverability and stability improvement for morphing aircraft wings. The bio-inspired wing model under consideration imitates the techniques used by birds to manipulate localized air flow through the installation of feather-like panels across the airfoil’s upper and lower surface, replacing the traditional wing’s surface and trailing edge flap. Each flap is designed to rotate into both the airfoil profile and inbound air flow, using a single degree of freedom about their individual hinge points located at 20%, 40%, 60% and 80% of the chord. This wing morphing technique offers flap configurations typically unattainable by traditional aircraft and enables some advantageous maneuvers, including reduced turning radii and aero-braking. Due to the number of potential configurations, a generalized adaptive panel method (APM) has been developed to model the pressure distribution using a series of constant-strength doublets along the airfoil surface. To accommodate for the wake regions generated by the unconventional wing profiles, viscous Computational Fluid Dynamics (CFD) simulations are performed to characterize these regions and identify their outer boundaries. The wake profile geometries are integrated into the APM, and are used to accurately model the aerodynamic influence of the wake. To calculate the drag generated by each configuration, Thwaites’ laminar and Head’s turbulent boundary layer methods are implemented to enable identification of flow transition and separation along the airfoil surface. The integration of these aerodynamic techniques allows the flight characteristics, including the pressure, friction, lift, drag, and moment coefficients, of each morphing airfoil configuration to be calculated. The computed aerodynamic coefficients are validated using experimental data from a 4′×1′×1′ test section in a low speed suction wind tunnel operating over a Reynolds Number range of 150,000–450,000.

Topics: Biomimetics , Wings
Commentary by Dr. Valentin Fuster
2013;():V002T06A008. doi:10.1115/SMASIS2013-3098.

Inspired by the characteristics of biological muscles, rubber muscle actuators (RMAs) are lightweight and compliant structures that deliver high power/weight ratios and are currently under investigation for use in soft robotics, prosthetics, and specialized aircraft. RMA actuation is accomplished by inflating the structure’s air bladder, which results in the contraction of the muscle. In this proceedings paper, we describe the use of gaseous products from enzymatically-catalyzed reactions to pressurize and drive the motion of RMAs. Specifically, this paper details the power envelope of RMAs driven by the urease-catalyzed production of CO2, under dynamic loading conditions. The use of enzymatically catalyzed, gas-producing reactions is advantageous for powering RMAs, as these systems may be self-regulating and self-regenerating. Reaction design parameters for sizing the gas source to RMA power requirements and power envelope results are reported for gas-powered actuator dynamics tested on a linear motion test assembly. The power response to increasing loads reflects the partial pressure over the reaction slurry; therefore, the chemistry and reactor scale affect the entire structure’s efficiency. We outline the reactor space-time design constraints that facilitate a tailored power response for urease catalyzed gas generation sources.

Topics: Actuators , Muscle
Commentary by Dr. Valentin Fuster
2013;():V002T06A009. doi:10.1115/SMASIS2013-3113.

Networks of biomolecular unit cells are proposed as a new type of biologically inspired intelligent materials. These materials are derived from natural cellular mechanics and aim to improve current biologically-inspired technologies by recreating the desired systems from the basic building block of the natural world; the cell. The individual biomolecular unit cell is able to replicate natural cellular abilities through a combination of lipid bilayer membranes containing embedded proteins and peptides. While individual unit cells offer an ideal testing environment for demonstrating proofs of concept, more advanced abilities require larger networks, utilizing cell-to-cell interactions.

The cell-to-cell interactions often involve multiple modes of communication, which have been identified for this paper as primarily electrical, chemical, and mechanical phenomenon. Previous modeling efforts have incorporated the electrical portion through equivalent circuit models, but these lack the ability to fully explain some of the network characteristics. A new formulation is presented here to illustrate how these three classes of phenomenon may be coupled to achieve various engineering design goals.

Commentary by Dr. Valentin Fuster
2013;():V002T06A010. doi:10.1115/SMASIS2013-3120.

Baffle shapes are commonly used in engineered devices to interface sound sources with the free field. Examples are acoustic horns seen in megaphones and horn-loaded loudspeakers. Typical for these devices are simple, static shapes that serve primarily an impedance-matching function. Diffracting baffles linked to a sound source are also common in the biosonar system of bats. In particular in bat groups that emit their ultrasonic pulses nasally, the nostrils are always surrounded by some baffle shape. This is the case across several large and diverse bat families such as horseshoe bats (Rhinolophidae), Old World leaf-nosed bats (Hipposideridae), and New World leaf-nosed bats (Phyllostomidae). However, biosonar baffles differ from their technical counterparts in two important ways: They typically have a much greater geometrical complexity and they are capable of non-rigid shape changes over time. Although simple horn shapes can be found in the noseleaves of many bat species, they are rarely as plain and regular as in megaphones and other technical applications of acoustical horns. Instead, the baffles are broken up into several parts that are frequently augmented with intricate local shape features such as ridges, furrows, and spikes. Furthermore, we have observed that in species belonging to the horseshoe bats and the related Old World leaf-nosed bats these local shape features are often not static, but can undergo displacements as well as non-rigid deformations. At least some of these dynamic effects are not passive byproducts of e.g., sound production or exhalation, but due to specific muscular actuation that can be controlled by the animals. To study these intricate, dynamic baffles as inspirations for smart structures, we have recreated the degrees of freedoms that Old World leaf-nosed bats have in deforming their noseleaves in a digital model using computer animation techniques. In its current form, our model has 6 degrees of freedom that can be used to test interactions between different motions using actuation patterns that occur in life as well as patterns that have not been observed, but could aid understanding. Because of the high-dimensional parameter space spanned by the different degrees of freedom, a high-performance computing platform has been used to characterize the acoustic behavior across a larger number of deformed no seleaf shapes. A physical test bed is currently under construction for implementing baffle motions that have been found to result in interesting changes of the acoustic device characteristics and could hence be of use to engineering applications.

Commentary by Dr. Valentin Fuster
2013;():V002T06A011. doi:10.1115/SMASIS2013-3130.

The research presented in this paper investigates the relationship between fluid flow characteristics in an artificial cochlear environment and artificial hair cell sensor response. First, a lipid bilayer-based hair cell sensor is created to model the inner hair cells of the human cochlea. The artificial cochlear environment is then fabricated to recreate the pulsating fluid flow around the artificial inner hair cell stereocilia. Mechanical excitation creates sinusoidal fluid flows in the artificial cochlear environment at a range of frequencies determined by the response of the hair cell sensor in air. For excitation frequencies at and below 40 Hz, the response of the hair cell sensor is approximately equal to the control case having no bilayer. At these low frequencies, bilayer dynamics do not appear to lead to current generation. At frequencies at and above 70 Hz, and in the absence of an externally applied DC offset across the bilayer, the hair cell sensors featuring a bilayer generate up to double the RMS current. Therefore, for excitation frequencies at and above 70 Hz, bilayer dynamics play a significant role in hair cell sensor response. Further testing of the hair cell sensor shows that applying a DC offset across the bilayer increases the peak-to-peak sensor output by up to a factor of 80.

Commentary by Dr. Valentin Fuster
2013;():V002T06A012. doi:10.1115/SMASIS2013-3132.

Synthetic lipid bilayers provide a cell-inspired environment for studying the functions of biomolecules. The regulated attachment method (RAM) is one method for forming liquid-supported lipid bilayers — known as droplet interface bilayers (DIBs) — that form at the interface of lipid-encased aqueous volumes in oil. While RAM allows for independent control of the aqueous phases on both sides of the membrane and provides a convenient way to control the size of the bilayer, previous studies utilizing this technique have been performed exclusively at room temperature. The goal of this research is to incorporate proportional-integral (PI) feedback control of temperature within the flexible RAM substrate with initial efforts focused on heating above room temperature. The proposed system includes a resistive etched-foil heating element and wire-type thermocouples for point-wise temperature measurement in standard RAM substrates. Open loop heating tests are used to map the magnitudes of steady state temperature distributions within the substrate and characterize the dynamic heating response. These tests show that a first-order heating model accurately describes transient temperature responses to heater power inputs. A one-probe configuration is found to provide measurements that are within <1°C of temperature measured at the bilayer region. The optimized probe configuration is used in PI feedback control, where the closed loop system is found to track the desired temperature to within +/−0.3°C. Experiments of temperature control with aqueous lipid droplets present permit electrical measurements of bilayer area without increasing background noise. Using this platform, we study the effect of temperature on the stability and size of a diphytanoyl phosphatidylcholine (DPhPC) lipid bilayer, and we observe that increasing the temperature of the bilayer from room temperature to 30°C results in a 30% decrease in the area of the membrane.

Topics: Feedback , Heating
Commentary by Dr. Valentin Fuster
2013;():V002T06A013. doi:10.1115/SMASIS2013-3134.

Droplet-based biomolecular arrays form the basis for a new class of bioinspired material system, whereby decreasing the sizes of the droplets and increasing the number of droplets can lead to higher functional density for the array. In this paper, we report on a non-microfluidic approach to form and connect nanoliter-to-femtoliter, lipid-coated aqueous droplets in oil to form micro-droplet interface bilayers (μDIBs). Two different modes of operation are reported for dispensing a wide range of droplet sizes (2–200μm radius). Due to the high surface-area-to-volume ratios of microdroplets at these length scales, droplet shrinking is prominent, which affects the stability and lifetime of the bilayer. To better quantify these effects, we measure the shrinkage rates for 8 different water droplet/oil compositions and study the effect of lipid placement and lipid type on morphological changes to μDIBs.

Topics: Sensors , Drops , Biomimetics
Commentary by Dr. Valentin Fuster
2013;():V002T06A014. doi:10.1115/SMASIS2013-3136.

We investigate taking advantage of the lightweight, compliant nature of fluidic artificial muscles to create variable recruitment actuators in the form of artificial muscle bundles. Several actuator elements at different diameter scales are packaged to act as a single actuator device. The actuator elements of the bundle can be connected to the fluidic control circuit so that different groups of actuator elements, much like individual muscle fibers, can be activated independently depending on the required force output and motion. This novel actuation concept allows us to save energy by effectively selecting the size of the actuators on the fly based on the instantaneous required load, versus the traditional method wherein actuators are sized for the maximum required load, and energy is wasted by oversized actuators most of the time. This design also allows a single bundled actuator to operate in substantially different force regimes, which could be valuable for robots that need to perform a wide variety of tasks and interact safely with humans. This paper will propose this actuator concept and show preliminary results of the design, fabrication, and experimental characterization of three such bioinspired variable recruitment actuator prototypes.

Topics: Muscle
Commentary by Dr. Valentin Fuster
2013;():V002T06A015. doi:10.1115/SMASIS2013-3141.

Recently, researchers have developed a method to construct a membrane-based hair cell sensor that generates a measurable current in response to physical disturbance of the hair. Representing the cell membrane, a phospholipid bilayer is formed at the interface of two lipid-encased hydrophilic volumes and a hair is located in a center of one of the volumes act a shaking element. In this work, we study the current generated by free vibration of the hair in a revised hair cell embodiment that uses a hair that is physically supported by the surrounding substrate. The current generated by the sensor is measured by a patch clamp amplifier, and the net charge displaced across the membrane during motion of the hair is computed. Experiments performed with a complete hair cell sensor and various control cases that lack a bilayer indicate that the current measured at 0mV applied across the membrane is due to vibration of the positive electrode that changes the local electromagnetic field. Experiments conducted with both geland liquid-supported membranes indicate that gel-supported membranes have a higher sensitivity of (0.066 pC/mV) than liquid-supported membranes (0.015 pC/mV) as the applied voltage increases. Lastly, the motion of the tip of the hair is imaged using a high-speed camera. This test shows that the hair oscillates at the same frequency observed in the measured current traces, which indicates that transverse bending of the bilayer is the cause for the time rate of change in capacitance in the membrane that produces a voltage-dependent current.

Topics: Sensors , Membranes
Commentary by Dr. Valentin Fuster
2013;():V002T06A016. doi:10.1115/SMASIS2013-3148.

An artificial hair cell sensor imitates the function of cilia in natural hair cells in order to detect surrounding fluid displacement. Here, a novel structure for creating artificial hair cell sensors uses established methods of creating lipid bilayers at the interfaces of millimeter scale hydrogel shapes. This paper describes the fabrication of the sensor components and the manner in which they are assembled and tested. The hair’s vibration can be detected by monitoring changes in the current produced by mechanical fluctuations in the bilayer. The cross-sectional geometry of the hair can be changed to enable directional sensitivity. Spectral analysis of the sensor current response indicates that frequencies and magnitudes change when a flattened hair is excited in different directions. Finally, the sensor is shown to become more sensitive with applied potential across the bilayer. Results agree with similar studies on this phenomenon.

Commentary by Dr. Valentin Fuster
2013;():V002T06A017. doi:10.1115/SMASIS2013-3189.

The hair cells in the cochlea are responsible for transforming sound-induced vibration into electrical signals. Damage to these hair cells is among the most common forms of hearing loss in the developed world. Researchers have studied various artificial hair cell (AHC) designs for replacing these hair cells. One such method uses piezoelectric beams to mimic the hair cell’s mechanoelectrical transduction. A piezoelectric beam will produce an electric potential from an applied sound pressure. In the literature, the response of the cochlea to sound pressures is often described using tuning curves. Tuning curves plot the sound pressure level at a given frequency which produces a particular displacement, velocity, or neuron firing rate. The work presented here examines using piezoelectric AHC’s to mimic cochlear hair cells by creating tuning curves of constant tip velocity and voltage. A piezoceramic (PZT) beam and a piezo film (PVDF) bending sensor are examined. An output feedback controller based on PID control is developed to vary the sound pressure from a speaker to create tuning curves for the piezoelectric AHC’s. The tuning curves for the piezoelectric beams are compared to measurements obtained from the biological cochlea.

Commentary by Dr. Valentin Fuster
2013;():V002T06A018. doi:10.1115/SMASIS2013-3202.

Selective rejection of dissolved salts in water is achieved by large pressure gradient driven flows through tortuous structures and cylindrical nanopores. The flow rate through the membrane is dependent on the area of the membrane and pressure gradient that can be sustained by the membrane. The electrical power required for generating large pressure gradients increases the operational cost for desalination units and limits application of contemporary technologies in a wide variety of applications. Due to this limitation, small scale operation of these desalination systems is not economical and portable. Further, recently proposed desalination systems using carbon nanotubes and nanofluidic diodes have limited lifetime due to clogging and fouling from contaminants in feed water. In order to develop a desalination system that is not limited by cost, scale of operation and application, an active nanopore membrane that uses multiphysics interactions in a surface-functionalized hyperboloidal nanopore is developed. An active nanopore is a shape-changing hyperboloidal pore that is formed in a rugged electroactive composite membrane and utilizes coupled electrostatic, hydrodynamic and mechanical interactions due to reversible mechanical oscillations between the charged pore walls and dissolved ions in water for desalination. This novel approach takes advantage of the shape of the pore to create a pumping action in the hyperboloidal channel to selectively transport water molecules. In order to demonstrate the applicability of this novel concept for water desalination, the paper will use a theoretical model to model the ion rejection properties and flow rate of purified water through an active nanoporous membrane. This article examines the effect of the geometry of the nanopore and frequency of operation to reject dissolved ions in water through a multiphysics model. It is estimated that the neck diameter of the active nanopores is the most dominant geometrical feature for achieving ion rejection, and the flux linearly increases with the frequency of operation (between 2–50Hz). The threshold neck diameter of the nanopore required for achieving rejection from multiphysics simulation is observed to be 100nm. The flux through the membrane decreases significantly with decreasing diameter and becomes negligible at 10nm effective neck diameter.

Topics: Membranes
Commentary by Dr. Valentin Fuster
2013;():V002T06A019. doi:10.1115/SMASIS2013-3210.

Pneumatic artificial muscles (PAMs) are a relatively common type of lightweight, fluid power actuation. Some disadvantages of PAMs include the compressibility of the working fluid and low damping. These characteristics result in low efficiencies, poor dynamic response, as well as undesired oscillations of the actuators. This paper presents utilizing hydraulic liquid as the working fluid instead of compressed air. Hydraulic operation resulted in almost triple the efficiency of pneumatic operation. The artificial muscles are experimentally characterized both quasi-statically and dynamically. The quasi-static experiments include the tension-strain relationship as a function of pressure, and an actuator net work efficiency analysis. The dynamic tests consist of a free vibration experiment to determine the change in effective spring constant and damping terms. These experiments are conducted for both PAMs and HAMs (hydraulic artificial muscles), and the results are presented herein.

Topics: Fluids , Actuators , Muscle
Commentary by Dr. Valentin Fuster
2013;():V002T06A020. doi:10.1115/SMASIS2013-3214.

Recent studies of polypyrrole (PPy) electrodes have been increasing the interfacial surface area in order to increase electrochemical performance. We present a novel method of electropolymerizing PPy doped with dodecylbenzenesulfonate (DBS) referred to as biotemplating. A biotemplated conducting polymer utilizes phospholipid vesicles in order to form a three dimensional structure with a sponge-like shape. The vesicles, measuring 1–2 μm in diameter, are added in situ with the polymerization solution. They become enveloped while maintaining their structure during electropolymerization of PPy(DBS). The result of this structure is a significant increase in surface area compared to current techniques. There are several advantages in using biotemplated conducting polymers as battery electrodes. Compared to a planar PPy(DBS) membrane, biotemplated PPy(DBS) membranes have a roughly 50% increased storage capacity. There is an expected reduction in volumetric expansion during ion ingress/egress into the polymer backbone. This reduction would result in decreased fatigue loading and improving cyclability. Further, biotemplated PPy(DBS) membranes can be fabricated into thin structures with increased flexibility, allowing them to be rolled into various packaging sizes. In this article, the charge density of a biotemplated PPy(DBS) membrane as a function of charging and discharging currents is compared to a planar PPy(DBS) membrane. The structural enhancement offers systemic advantages by providing higher volumetric energy density and decreased fatigue loading for applications involving conducting polymer electrodes.

Topics: Membranes
Commentary by Dr. Valentin Fuster
2013;():V002T06A021. doi:10.1115/SMASIS2013-3218.

Conducting polymers undergo volumetric expansion through redox-mediated ion exchange with its electrolytic environment. The ion transport processes resulting from an applied electrical field controls the conformational relaxation in conducting polymer and regulates the generated stress and strain. In the last two decades, significant contributions from various groups have resulted in methods to fabricate, model and characterize the mechanical response of conducting polymer actuators in bending mode. An alternating electrical field applied to the polymer electrolyte interface produces the mechanical response in the polymer. The electrical energy applied to the polymer is used by the electrochemical reaction in the polymer backbone, for ion transport at the electrolyte-polymer interface and for conformational changes to the polymer. Due to the advances in polymer synthesis, there are multitudes of polymer-dopant combinations used to design an actuator. Over the last decade, polypyrrole (PPy) has evolved to be the most common conducting polymer actuator. Thin sheets of polymer are electrodeposited on to a substrate, doped with dodecylbezenesulfonate (DBS-) and microfabricated into a hermetic, air operated cantilever actuator. The electrical energy applied across the thickness of the polymer is expended by the electrochemical interactions at the polymer-electrolyte interface, ion transport and electrostatic interactions of the backbone. The widely adopted model for designing actuators is the electrochemically stimulated conformational relaxation (ESCR) model. Despite these advances, there have been very few investigations into the development of a constitutive model for conducting polymers that represent the input-output relation for chemoelectromechanical energy conversion. On one hand, dynamic models of conducting polymers use multiphysics-based non-linear models that are computationally intensive and not scalable for complicated geometries. On the other, empirical models that represent the chemomechanical coupling in conducting polymers present an over-simplified approach and lack the scientific rigor in predicting the mechanical response. In order to address these limitations and to develop a constitutive model for conducting polymers, its coupled chemomechanical response and material degradation with time, we have developed a constitutive model for polypyrrole-based conducting polymer actuator. The constitutive model is applied to a micron-scale conducting polymer actuator and coupling coefficients are expressed using a mechanistic representation of coupling in polypyrrole (dodecylbenzenesulfonate) [PPy(DBS)].

Commentary by Dr. Valentin Fuster
2013;():V002T06A022. doi:10.1115/SMASIS2013-3226.

This paper describes a fully coupled finite element simulation of the chemo-electro-mechanical effect of the swelling characteristic of a human intervertebral disc. The swelling behavior of human intervertebral disc is strongly influenced by various environmental stimuli such as concentration of the mobile ions, fixed charges on fibrous material, and pH of the surrounding bio-fluid. The swelling behavior can be described by three physical partial differential equations. These equations are-Nernst-Plank for chemical species transport, Poisson’s for the balanced fixed charges inside the vertebral disc, and mechanical field for balanced osmotic pressure and resulting expansion of the disc. The converged solution of the 2D finite element simulation was achieved by full coupling among these equations in moving mesh domain. The effects of several important physical conditions, such as concentration of mobile ions, pH change in surrounding bio-fluid, electrical charge balance, and the expansion/shrinkage of vertebral disc are simulated. The simulation results are discussed in detail.

Commentary by Dr. Valentin Fuster
2013;():V002T06A023. doi:10.1115/SMASIS2013-3235.

Advanced fiber reinforced ceramic composite having self-healing function (shFRC) has been developed. The composite includes the silicon carbide interlayer as healing agent at the interface between alumina fiber and alumina matrix. The healing agent interlayer caused the preferential fracture of the fiber/matrix interface and the interface fracture gave rise to the slip of the interface during crack propagation. Thereby the shFRC could exhibit a large deformation at the fracture and large fracture energy. Moreover, the high temperature oxidation of the healing agent made the interface delimitation rebounded by the formed oxide and the reaction heat. As a result, the maximum strength and the stiffness degraded by the interface delimitation could be recovered by the healing. Consequently, it was found that the shFRC containing the interlayer of the healing agent can survive the repeated crack propagation or initiation due to the large impact damage.

Commentary by Dr. Valentin Fuster
2013;():V002T06A024. doi:10.1115/SMASIS2013-3250.

This work presents a strategy to identify the optimal localized activation and actuation for a morphing thermally activated SMP structure or structural component to obtain a targeted shape change or set of shape features, subject to design objectives such as minimal total required energy and time. This strategy combines numerical representations of the SMP structure’s thermo-mechanical behavior subject to activation and actuation with gradient-based nonlinear optimization methods to solve the morphing inverse problem that includes minimizing cost functions which address thermal and mechanical energy, morphing time, and damage. In particular, the optimization strategy utilizes the adjoint method to efficiently compute the gradient of the objective functional(s) with respect to the design parameters for this coupled thermo-mechanical problem.

Topics: Design
Commentary by Dr. Valentin Fuster
2013;():V002T06A025. doi:10.1115/SMASIS2013-3261.

Design and actuation modes of IntraVAD assistive device for end stage congestive heart failure patients are discussed in this paper. Flexibility, biocompatibility and coupled behavior of Ionic Polymer Metal Composites and Shape Memory Alloys allow replicating the motion of natural heart to address the cardiac deficiency. The squeezing motion of the heart is approximated by propulsion mechanism of a jelllyfish, while the rising-twisting motion of the heart is augmented by upward-downward motion of a cone shaped structure. These motion mechanisms may be combined or used separately, in order to create various blood flow regimes and provide different levels of support for each individual. Not only as actuators, but SMAs and IPMCs may be utilized as sensors to provide feedback from instantaneous status of the device to the controller. A device embodiment is introduced and followed by discussion on IPMC and antagonistic two-way SMA actuators in order to explain how actuation modes are delivered.

Commentary by Dr. Valentin Fuster
2013;():V002T06A026. doi:10.1115/SMASIS2013-3262.

Pneumatic artificial muscles (PAMs) are used in robotics applications for their light-weight design and superior static performance. Additional PAM benefits are high specific work, high force density, simple design, and long fatigue life. Previous use of PAMs in robotics research has focused on using “large,” full-scale PAMs as actuators. Large PAMs work well for applications with large working volumes that require high force and torque outputs, such as robotic arms. However, in the case of a compact robotic hand, a large number of degrees of freedom are required. A human hand has 35 muscles, so for similar functionality, a robot hand needs a similar number of actuators that must fit in a small volume. Therefore, using full scale PAMs to actuate a robot hand requires a large volume which for robotics and prosthetics applications is not feasible, and smaller actuators, such as miniature PAMs, must be used. In order to develop a miniature PAM capable of producing the forces and contractions needed in a robotic hand, different braid and bladder material combinations were characterized to determine the load stroke profiles. Through this characterization, miniature PAMs were shown to have comparably high force density with the benefit of reduced actuator volume when compared to full scale PAMs. Testing also showed that braid-bladder interactions have an important effect at this scale, which cannot be modeled sufficiently using existing methods without resorting to a higher-order constitutive relationship. Due to the model inaccuracies and the limited selection of commercially available materials at this scale, custom molded bladders were created. PAMs created with these thin, soft bladders exhibited greatly improved performance.

Commentary by Dr. Valentin Fuster
2013;():V002T06A027. doi:10.1115/SMASIS2013-3311.

A coupled electro-aero-mechanical modeling and optimization scheme for two solid-state piezocomposite variable-camber wing concepts is presented. The proposed concepts employ a continuous inextensible surface, simple boundary conditions and surface bonded piezoelectric actuators. The partially-active surfaces are designed to have sufficient bending stiffness in the chordwise and spanwise directions to sustain shape under aerodynamic loading. In contrast, the in-plane stiffness is relatively high; however the necessary deformations that are required to change the aerodynamic response can still be attained while maintaining the surface perimeter constant. Coupled with the continuous boundary conditions and the spar structure, the proposed concepts can achieve significant change in aerodynamic response quantified in terms of lift coefficient and lift-to-drag ratio under aerodynamic loading. A coupled analysis of the fluid-structure interaction is employed assuming static-aeroelastic behavior which allows the realization of designs that can sustain aerodynamic loads. Two prototypes are briefly presented.

Commentary by Dr. Valentin Fuster
2013;():V002T06A028. doi:10.1115/SMASIS2013-3328.

Pneumatic Artificial Muscles (PAMs) are remarkable for their simplicity, light weight, high stroke, and high force. PAMs are used extensively in robotics applications where actuator bandwidth requirements are relatively low (e.g., < 1 Hz) compared to aerospace applications where higher bandwidth is needed (e.g., as high as 30 Hz in rotor vibration control). Because PAMs couple large stroke with high specific actuation force, adapting PAMs to aerospace applications may provide a substantial gain in performance over conventional hydraulic and pneumatic actuators. This study develops a semi-empirical, nonlinear, pneumo-mechanical analysis of the time histories of pressure, force, and displacement, which is validated using experimental response data from a single PAM working against a spring and mass. A linear proportional + integral + derivative (PID) controller was then tuned analytically to achieve command following of sinusoids. Frequency responses are obtained via both simulation and experiment, and the ability to track relatively high frequency control inputs is demonstrated for periodic motions up to 24 Hz.

Topics: Modeling , Muscle
Commentary by Dr. Valentin Fuster
2013;():V002T06A029. doi:10.1115/SMASIS2013-3344.

Fluidic flexible matrix composite (F2MC) tubes are fiber-reinforced tubes that have been designed to change structural characteristics (e.g., shape, stiffness, damping, actuation force, etc.) based on the control of fluid flow and pressure inside the tubes. In the current investigation, miniature F2MC tubes (2 mm diameter) are designed and evaluated. The tubes are made with fine steel wire and a flexible polyurethane matrix. Tubes with reinforcement angles of ±40 and ±24 degrees relative to the longitudinal axis were evaluated in terms of blocked force and free strain versus internal pressure and axial modulus of elasticity. Sheets of multiple, unidirectionally aligned tubes positioned side by side and potted into a surrounding compliant matrix material were evaluated as well. Encouraging agreement with elasticity solutions based on infinitely long multi-layer tubes with internal pressurization was observed. Over the long term, this line of research is aimed at the development of thin skins for structures that can change shape and stiffness differently as a function of direction.

Commentary by Dr. Valentin Fuster

Energy Harvesting

2013;():V002T07A001. doi:10.1115/SMASIS2013-3020.

Harvesting energy from ambient vibrations in order to power autonomous sensors is a challenging issue. The aim of this work is to compare the power output from an innovative multi-frequency fractal-inspired piezoelectric converter to that from a traditional multi-cantilever piezoelectric converter. The converters are designed in order to give the same eigenfrequencies in a given range and a prototype of both is built using commercial materials. The experimental tests investigate both the effect of the acceleration and of the resistive load applied to the converters for each of the three eigenfrequencies in the range between 0 and 120 Hz. The fractal-inspired converter exhibits a significantly higher specific output power at the first and third of the eigenfrequencies investigated.

Commentary by Dr. Valentin Fuster
2013;():V002T07A002. doi:10.1115/SMASIS2013-3030.

Conventional Thermoacoustic-Piezoelectric (TAP) energy harvesters convert thermal energy, such as solar or waste heat energy, directly into electrical energy without the need for any moving components. The input thermal energy generates a steep temperature gradient along a porous medium. At a critical threshold of the temperature gradient, self-sustained acoustic waves are developed inside an acoustic resonator. The associated pressure fluctuations impinge on a piezoelectric diaphragm, placed at the end of the resonator. The reverse phenomenon results in piezo-driven thermoacoustic refrigerators (PDTARs). A pressure wave driven by a piezo-speaker induces a temperature gradient across the porous body. In this study, the TAP harvester and the PDTAR are coupled with auxiliary elastic structures in the form of simple spring-mass systems to enhance their performance. The proposed addition is referred to as a dynamic magnifier and has been shown in different areas to amplify significantly the deflection of vibrating structures. A comprehensive model of the dynamically magnified thermoacoustic-piezoelectric (DMTAP) system has been developed earlier that includes equations of motions of the system’s mechanical components, the harvested voltage, the mechanical impedance of the coupled structure at the resonator end as well as the equations necessary to compute the self-excited frequencies of oscillations inside the acoustic resonator. Theoretical results confirmed significant amplification of the harvested power is feasible if the magnifier’s parameters are properly chosen. The performance of experimental prototypes of a DMTAP harvester and a PDTAR with a dynamic magnifier are examined here. The obtained experimental findings are validated against the theoretical results. Dynamic magnifiers serve as a novel approach to enhance the effectiveness of thermoacoustic energy harvesting and refrigeration.

Commentary by Dr. Valentin Fuster
2013;():V002T07A003. doi:10.1115/SMASIS2013-3050.

A digital energy harvester that captures electrical energy from complicated random or multimodal vibrations is proposed. The novel energy harvester is digital, autonomous, and controlled by a self-powered microprocessor. The digital self-powered microprocessor automatically and synchronously changes the circuit components with the vibration phase, and can therefore achieve autonomous harvesting. The multifunctional and self-controlled microprocessor is only driven by the voltage of the piezoelectric transducer, and no external power is required. The harvester exhibits great potential and versatility and is applicable to many machines and devices.

Commentary by Dr. Valentin Fuster
2013;():V002T07A004. doi:10.1115/SMASIS2013-3063.

Discrete animal-mounted sensors and tags have a wide range of potential applications for researching wild animals and their environments. The devices could be used to monitor location, metabolic output, or used as environmental monitoring sentinels. These applications are made possible by recent decreases in the size, mass, and power consumption of modern microelectronics. Despite these performance increases, for extended deployments these systems need to generate power in-situ. In this work, we explore a device that was recently deployed to test the concept of vibrational piezoelectric energy harvesting on flying birds. We explain the development of the device and introduce test results conducted on flying pigeons (Columba livia). The 12 g testing device consisted of a miniature data acquisition system and a piezoelectric energy harvester. The system recorded both the harvested power and the in-flight accelerations of the bird. The energy harvester included a wireless receiver, battery and linear servo. By remotely actuating the linear servo, we were able to arrest the energy harvester for portions of the flight. In doing so, we will be able to compare flight accelerations of a bird with a simple proof mass and with a dynamic mass without having to stop the flight of the bird. The comparison of these two cases allows for the assessment of the feasibility of employing vibrational energy harvesting on a flying bird. We present the initial results of this testing with regard to the harvested power and the in-flight acceleration profiles.

Commentary by Dr. Valentin Fuster
2013;():V002T07A005. doi:10.1115/SMASIS2013-3066.

In this work, we have combined a micro-piezoelectric energy harvester with a dedicated interfacing circuit using the non-linear switch harvesting techniques based on the concept of SSH (synchronized switch harvesting). We especially focused on the power enhancement effect of the switching technique on micro-power generators. The micro-piezoelectric energy harvester that was used in this work is based on a stainless steel substrate, which largely improved the power output capability of the device. The resonant frequency of the energy harvesting device is 117 Hz, giving a voltage output of 3.85 V under the acceleration of 0.05 g. The overall size of the harvesting device is merely 8*6*0.5 mm3, including the proof mass. In order to further enhance the power generation abilities of the micro-generator, non-linear electrical interface circuits have also been designed and tested on two devices. According to the value of the figure of merit given by the product of the squared coupling coefficient k2 by the mechanical quality factor QM, a significant power gain compared to standard energy harvesting interface up to 3.13 has been tested for the device featuring a k2QM value of 0.17. A gain of 1.85 for a device with a k2QM value of 0.42 was also found. All of which were in good agreement with theoretical predictions. Furthermore, in order to be as close as possible to the realistic implementation of the micro-generators, the above mentioned nonlinear interface circuit were implemented in a self-powered design (i.e., without requiring an external energy source) using a very small part of the energy available generated from the piezoelectric energy harvester. Using the self powered technique, the overall system was available to provide 91.4 μW, with accelerations around 0.75 g, under the condition of k2QM = 0.72, and the power gain of 2.03.

Commentary by Dr. Valentin Fuster
2013;():V002T07A006. doi:10.1115/SMASIS2013-3067.

This paper presents the modeling and control of a Continuously Variable Planetary (CVP) transmission in a wind turbine system. The primary purpose of this paper is to evaluate its effectiveness for mechanically decoupling the variable speed turbine rotor from the grid tied induction generator. It is expected that a CVP controlled wind turbine can take advantage of the grid tied induction generator without the use of an inverter, while optimizing the blade speed aerodynamically. This system also expands its operating range making it possible to track the optimal tip speed ratio over a wider wind speed range, which allows higher power to be captured from the wind. System characteristics have been studied by simulating an 8kW horizontal axis wind turbine in a MatLab/Simulink® environment. Experimental results have been included to verify the model of the system. Analyses conducted show that the continuously variable transmissions are potential candidates for small wind turbine applications.

Commentary by Dr. Valentin Fuster
2013;():V002T07A007. doi:10.1115/SMASIS2013-3076.

Traditionally, vibration-based energy harvesters have been designed for specific base excitation frequencies by matching their natural frequencies. However, harvesting energy from common human motions is challenging because the low frequencies involved are incompatible with small, light-weight transducers, which have much higher natural frequencies. By using the frequency up-conversion method, a vibration-based, nonlinear, magnetically excited energy harvester exhibits efficient, broadband, frequency-independent performance.

A complete model is provided for an energy harvester utilizing the frequency up-conversion method that defines the relationship between the enclosure excitation, the base excitation and the stationary magnets, where the base of the beam is mounted elastically inside an enclosure. The average power output of a vibration-based energy harvester with frequency up-conversion is analyzed using artificial and naturally occurring base excitations such as sinusoidal and walking motions, respectively. Simulations are provided to demonstrate the broadband capabilities of vibration-based energy harvesters with frequency up-conversion, especially for driving frequencies lower than the fundamental frequency, where significant increase in power output are observed when utilizing frequency up-conversion. In addition, the advantages and limitations of approximating a range of natural base excitations with a set of orthogonal basis functions are explored, which provides motivation for Wavelets Analysis. Finally, a procedure is proposed to determine the maximum expected power output.

Commentary by Dr. Valentin Fuster
2013;():V002T07A008. doi:10.1115/SMASIS2013-3110.

The analytical modeling and experimental investigation of a nonlinear electromagnetic rotational energy harvester, which can harvest power from rotary and translational excitations, are presented. Some application of energy harvesting such as energy harvesting for tire pressure sensing require an energy harvester which is efficient in generating power from rotational ambient vibrations. The majority of literature on vibration energy harvesting assumes that the ambient excitations are along a single axis. The vibrations from human motion or rotary machines have two components of translational motion as well as a strong rotary motion. The energy harvesting device studied in this paper is a pendulum like device. The base excitations result in rotations of a pendulum. The pendulum is connected to a direct current micro generator. The rotational vibrations of the pendulum generates electricity through the DC generator. Since the energy harvester is responsive to both translational and rotational base excitations, it is called Hybrid Rotary-Translational (HRT) generator.

In this paper a small size HRT harvester is introduced and modeled. The model is used to investigate the relation between the frequency and the amplitude of base vibrations on the vibrations and power generation characteristics of the HRT system. For each frequency and amplitude of vibrations the coexistence of multiple solutions and their basin of attractions are investigated. Three types of ambient excitations are studied: rotational, translational along the direction of gravity, and translational normal to the direction of the gravity.

Commentary by Dr. Valentin Fuster
2013;():V002T07A009. doi:10.1115/SMASIS2013-3115.

This paper presents theoretical and experimental investigations into the potential of utilizing a piezoaeroelastic micropower generator to harvest energy from the combination of an external base excitation and an aerodynamic load. In particular, a harvester consisting of a rigid airfoil supported by a flexural piezoelectric beam and a torsional spring is placed in an incompressible air flow and subjected to an external harmonic base excitation in the plunge direction. Electromechanical equations describing the nonlinear system are given along with theoretical simulations. The performance of the piezoaeroelastic generator is studied experimentally below and above the flutter speed and found to exhibit qualitative agreement with the theory. Below the flutter speed, the response of the harvester is observed to be always periodic with the air flow serving to amplify the influence of the base excitation on the response by reducing the effective stiffness of the system, and hence, increasing the RMS output power. Beyond the flutter speed, the harvester’s response and its performance were observed to depend on the nearness of the excitation frequency to the frequency of the self-sustained oscillations induced by the flutter instability and the magnitude of the base excitation. When the base excitation is small and/or the excitation frequency is not close to the frequency of the self-sustained oscillations, the response of the harvester is two-period quasiperiodic with amplitude modulation due to the presence of two incommensurate frequencies. This amplitude modulation reduces the RMS output power. On the other hand, when the frequency of excitation is close to the frequency of the self-sustained oscillations and/or the amplitude of excitation is large enough to quench the quasiperiodic behavior, the response becomes periodic and the output power increases exhibiting little dependence on the base excitation.

Commentary by Dr. Valentin Fuster
2013;():V002T07A010. doi:10.1115/SMASIS2013-3122.

In this paper, we investigate a galloping piezoelectric energy harvester (GPEH) with a square bluff body. Comprehensive wind tunnel tests are conducted and experimental data are used to validate our analytical approximate solutions, which are derived from a coupled aero-electro-mechanical model. In addition, the effects of impact disturbances using a bump are investigated. The goal is to improve the performance of baseline GPEH. We expect to collect physical insight to design an optimal nonlinear GPEH configuration by placing bumps accordingly. Lessons learnt from this study will be used to improve the performance of future nonlinear GPEHs and lead to a practical device.

Commentary by Dr. Valentin Fuster
2013;():V002T07A011. doi:10.1115/SMASIS2013-3123.

In this paper, we demonstrate a novel miniature three-axis piezoelectric energy harvester. The energy harvester consists of four piezoelectric lead zirconate titanate cantilever beams, connector, proof mass, and mechanic frame. Through the connector, a special configuration with a well-constrained mechanism of the energy harvester is achieved. Due to the configuration/mechanism of the energy harvester, the Newton’s law of inertia and piezoelectric effect are utilized to convert the in-plane (either x-axis or y-axis) and out-of-plane (z-axis) environmental vibrations into voltage responses. This achieves energy harnessing from 3-axial environmental vibration.

Commentary by Dr. Valentin Fuster
2013;():V002T07A012. doi:10.1115/SMASIS2013-3125.

In this study, we investigate underwater energy harvesting from torsional vibration of a patterned ionic polymer metal composite (IPMC). The IPMC design consists of a rectangular polymer strip with patterned electrodes to split the top and bottom surfaces in two equal pairs. We focus on harmonic base excitation of an IPMC, which is modeled as a slender beam with thin cross section vibrating in a viscous fluid. Torsional vibrations with large–amplitude are described using a complex hydrodynamic function considering nonlinear hydrodynamic damping from the surrounding fluid. Along with the theoretical beam model, an electromechanical model is utilized to predict the IPMC electrical response from the torsional deformation of the beam. The integration of both models allows to predict the output voltage of the IPMC from the knowledge of the frequency and amplitude of base excitation. The theoretical predictions are validated against experiments.

Commentary by Dr. Valentin Fuster
2013;():V002T07A013. doi:10.1115/SMASIS2013-3127.

In this study, we seek to understand the feasibility of energy harvesting from the tail beating motion of a fish through active compliant materials. Specifically, we analyze energy harvesting from the undulations of a biomimetic fish tail hosting ionic polymer metal composites (IPMCs). The design of the biomimetic tail is specifically inspired by the morphology of the heterocercal tail of thresher sharks. We propose a modeling framework for the underwater vibration of the biomimetic tail, wherein the tail is assimilated to a cantilever beam with rectangular cross section. We focus on base excitation in the form of a superimposed rotation about a fixed axis and we consider the regime of moderately large–amplitude vibrations. In this context, the effect of the encompassing fluid is described through a nonlinear hydrodynamic function. The feasibility of harvesting energy from an IPMC attached to the vibrating structure is assessed and modeled via an electromechanical framework. Experiments are performed to validate the theoretical expectations on energy harvesting from the biomimetic tail.

Commentary by Dr. Valentin Fuster
2013;():V002T07A014. doi:10.1115/SMASIS2013-3137.

Vibration based energy harvesting has received extensive attention in the engineering community for the past decade thanks to its potential for autonomous powering small electronic devices. For this purpose, linear electromechanical devices converting mechanical to useful electrical energy have been extensively investigated. Such systems operate optimally when excited close to or at resonance, however, for these lightly damped structures small variations in the ambient vibration frequency results in a rapid reduction of performance. The idea to use nonlinearity to obtain large amplitude response in a wider frequency range, has shown the potential for achieving so called broadband energy harvesting. An interesting type of nonlinear structures exhibiting the desired broadband response characteristics are bi-stable composites. The bi-stable nature of these composites allows for designing several ranges of wide band large amplitude oscillations, from which high power can be harvested. In this paper, an analytical electromechanical model of cantilevered piezoelectric bi-stable composites for broadband harvesting is presented. The model allows to calculate the modal characteristics, such as natural frequencies and mode shapes, providing a tool for the design of bi-stable composites as harvesting devices. The generalised coupling coefficient is used to select the positioning of piezoelectric elements on the composites for maximising the conversion energy. The modal response of a test specimen is obtained and compared to theoretical results showing good agreement, thus validating the model.

Commentary by Dr. Valentin Fuster
2013;():V002T07A015. doi:10.1115/SMASIS2013-3139.

Vibration-to-electricity conversion has been heavily researched over the last decade with the ultimate goal of enabling self-powered small electronic components to use in wireless applications ranging from medical implants to structural health monitoring sensors. Regardless of the transduction mechanism used in transforming vibrational energy into electricity, the existing research efforts have mostly focused on deterministic or stochastic harvesting of direct vibrational energy available at a fixed location in space. Such an approach is convenient to design and employ linear and nonlinear vibration-based energy harvesters, such as base-excited cantilevers with piezoelectric laminates. Although the harvesting of local vibrations using linear and nonlinear devices has been well studied, there has been little effort to investigate power extraction from elastic waves propagating in host structures to gain a fundamental understanding of power flow and to best exploit not only standing but also traveling wave energy. This paper explores the problem of piezoelectric energy harvesting from one-dimensional bending waves involving propagating and evanescent components with a focus on infinitely long thin beams. A pair of electroded piezoelectric patches is implemented as the energy harvesting interface connected to a complex electrical load. An analytical modeling framework is given in order to relate the harvested power to incoming wave in the presence of a generalized resistive-reactive circuit. Effects of energy harvesting on the global wave dynamics as well as individual propagating and evanescent wave components are investigated with an emphasis on the wavelength matching concept. The electrical loading conditions for maximum power and efficiency are identified for several special cases in the low frequency range.

Topics: Waves , Circuits
Commentary by Dr. Valentin Fuster
2013;():V002T07A016. doi:10.1115/SMASIS2013-3145.

Vibration-based energy harvesting using cantilevered piezoelectric beam has been extensively studied over the last decade. In this study, as an alternative to resonant piezoelectric cantilevers, we studied multiple patch-based piezoelectric energy harvesting from multiple vibration modes of thin plates. Analytical electroelastic model of the multiple patch-based piezoelectric harvesters attached on a thin plate is provided based on distributed-parameter modeling approach for series and parallel configurations of the patches. An experimental setup is built with series-configuration of double patch-based harvesters attached on the surfaces of all-four-edges clamped (CCCC) rectangular aluminum plate. Analytical simulations and experimental validations of power generation of the harvesters are performed in a case study. The experimental and analytical frequency response functions (FRF) relating voltage output and vibration response to force input are obtained. The analytical model is validated by comparing analytical and experimental FRFs for a wide range of resistive electrical boundary conditions. The harvested power output across the various resistive loads is explored with a focus on the first four modes of the aluminum plate. Experimental and analytical results are shown to be in agreement for multiple patch-based piezoelectric energy harvesting from multiple vibration modes of thin plates.

Commentary by Dr. Valentin Fuster
2013;():V002T07A017. doi:10.1115/SMASIS2013-3165.

This paper introduces a novel vibration energy harvesting structure with a resonance frequency that is tunable over a large range using a simple compact mechanical adjustment that alters the structural stiffness. The frequency tuning requires minimal actuation that can be “turned off” while maintaining the new resonance frequency. Testing shows that the natural frequency can be adjusted from 32 Hz to 85 Hz. The structure is coupled with an electromagnetic transducer to generate power. Test results at varying excitation frequencies and amplitudes demonstrate tunable power generation over a very wide bandwidth. In addition to frequency tunability, the structure is a nonlinear softening spring, which provides the added benefit of a passively wider bandwidth for specific ranges of the design parameters.

Commentary by Dr. Valentin Fuster
2013;():V002T07A018. doi:10.1115/SMASIS2013-3176.

In this paper, the modeling and analysis of a nonlinear rectangular plate-like wing with embedded piezoceramics is presented for aeroelastic energy harvesting. The nonlinear electromechanical finite-element plate model is based on the von Karman plate assumptions while the unsteady aerodynamic model uses the doublet-lattice method (originally in frequency domain). The aerodynamic model is converted to the time domain by using Roger’s approximation. A load resistance is considered in the electrical domain of the problem. The set of nonlinear equations is solved with the iterative Newton-Raphson method and the generalized alpha method is used to numerically integrate the equations. Five different wing configurations with aspect ratios varying from one to five are investigated. The effect of the aspect ratio on the linear aeroelastic behavior is first investigated for the short circuit condition. Later, the nonlinear electroaeroelastic behavior is investigated for a range of load resistances and the different aspect ratios of the linear case. The effects of aspect ratio and load resistance on the cut-in speed of limit cycle oscillations (LCOs), on the range of airflow speeds of LCOs of acceptable amplitudes and also on the mechanical and electrical outputs of the generator are investigated.

Commentary by Dr. Valentin Fuster
2013;():V002T07A019. doi:10.1115/SMASIS2013-3179.

A hydraulic pressure energy harvester (HPEH) device, which utilizes a housing to isolate a piezoelectric stack from the hydraulic fluid via a mechanical interface, generates power by converting the dynamic pressure within the system into electricity. Prior work developed an HPEH device capable of generating 2187 microWatts from an 85 kPa pressure ripple amplitude using a 1387 mm3 stack. A new generation of HPEH produced 157 microWatts at the test conditions of 18 MPa static pressure and 394 kPa root-mean-square pressure amplitude using a 50 mm3 stack, thus increasing the power produced per volume of piezoelectric stack principally due to the higher dynamic pressure input. The stack and housing design implemented on this new prototype device yield a compact, high-pressure hydraulic pressure energy harvester designed to withstand 35 MPa. The device, which is less than a 2.54 cm in length as compared to a 5.3 cm length of a previous HPEH, was statically tested up to 21.9 MPa and dynamically tested up to 19 MPa with 400 kPa root-mean-square dynamic pressure amplitude. An inductor was included in the load circuit in parallel with the stack and the load resistance to increase the power output of the device. A previously developed electromechanical power output model for this device that predicts the power output given the dynamic pressure ripple amplitude is compared to the power results. The power extracted from this device would be sufficient to meet the proposed applications of the device, which is to power sensor nodes in hydraulic systems.

Commentary by Dr. Valentin Fuster
2013;():V002T07A020. doi:10.1115/SMASIS2013-3191.

Energy harvesting systems for structural health monitoring applications may be described by three stages: ambient energy transduction, electrical power conditioning, and data acquisition and transmission. Recent developments in low-power CMOS devices have allowed for expanded energy harvesting techniques by reducing the total power demand of sensor nodes.

This paper investigates the system-level interaction between a corrosion-based energy harvester and the low-power sensor node to which it is supplying power. An equivalent circuit model of the energy harvester is developed and the matched parameters (source voltage and equivalent series resistance) are used in the design of the power conditioning and wireless transmitter circuitry. Analysis of the power demand from the sensor node is used to determine the optimum data sampling parameters in terms of available supplied power for long-term in-situ sensing operations on a marine structure.

Commentary by Dr. Valentin Fuster
2013;():V002T07A021. doi:10.1115/SMASIS2013-3194.

Elastic instability, long considered mainly as a failure limit state or a safety guard against ultimate failure is gaining increased interest due to the development of active and controllable structures, and the growth in computational power. Mode jumping, or snap-through, during the postbuckling response leads to sudden and high-rate deformations due to generally smaller changes in the controlling load or displacement input to the system. A paradigm shift is thus emerging in using the unstable response range of slender structures for purposes that are rapidly increasing and diversifying, including applications such as energy harvesting, frequency tuning, sensing and actuation. This paper presents a finite element based numerical study on controlling the postbuckling behavior of fiber reinforced polymer cylindrical shells under axial compression. Considered variables in the numerical analyses include: the ply orientation and laminate stacking sequence; the material distribution on the shell surface (stiffness distribution); and the anisotropic coupling effects. Preliminary results suggest that the static and dynamic response of unstable mode branch switching during postbuckling can be fully characterized, and that their number and occurrence can be potentially tailored. Use of the observed behavior for energy harvesting and other sensing and actuation applications will be presented in future studies.

Commentary by Dr. Valentin Fuster
2013;():V002T07A022. doi:10.1115/SMASIS2013-3197.

Many signals of interest in the assessment of structural systems lie in the quasi-static range (frequency ≪ 1Hz). This poses a significant challenge for the development of self-powered sensors that are required not only to monitor these events but also to harvest the energy for sensing, computation and storage from the signal being monitored. This paper combines the use of mechanically-equivalent frequency modulators and piezo-powered threshold detection modules capable of computation and data storage with a total current less than 10nA. The system is able to achieve events counting for input deformations at frequencies lower than 0.1Hz.

The used mechanically-equivalent frequency modulators allow the transformation of the low-amplitude and low-rate quasi-static deformations into an amplified input to a piezoelectric transducer. The sudden transitions in unstable mode branch switching, during the elastic postbuckling response of slender columns and plates, are used to generate high-rate deformations. Experimental results show that an oscillating semi-crystalline plastic polyvinylidene fluoride (PVDF), attached to the up-converting modules, is able to generate a harvestable energy at levels between 0.8μJ to 2μJ.

In this work, we show that a linear injection response of our combined frequency up-converter / piezo-floating-gate sensing system can be used for self-powered measurement and recording of quasi-static deformations levels. The experimental results demonstrate that a sensor fabricated in a 0.5-μm CMOS technology can count and record the number of quasi-static input events, while operating at a power level significantly lower than 1μW.

Commentary by Dr. Valentin Fuster
2013;():V002T07A023. doi:10.1115/SMASIS2013-3199.

Converted energy from ambient loading in civil and mechanical structures is typically used as a viable alternative. Although, piezoelectric vibration harvesters have been widely used given their energy conversion ability, these elements exhibit a narrow natural frequency response range, thus considerably limiting the levels of harvestable power.

Recently our group has introduced the concept of using mechanically-equivalent frequency modulators that can transform the low-amplitude and low-rate service and ambient deformations into an amplified input to the piezoelectric transducer. The introduced methods allow energy generation and conversion within the unexplored quasi-static frequency range (≪ 1 Hz). The post-buckling behavior of bilaterally constrained columns was used for frequency up-conversion, and piezoelectric cantilever beams, attached to the columns, were used for energy conversion.

The introduced concept was experimentally validated and finite element simulations were developed to evaluate the effect of system parameters (stiffness, thickness, and walls gap) on the position of the snap-through transition events and the levels of force-displacement at the multiple-equilibrium configurations. It was shown that the considered system parameters can determine the absolute levels of force and displacement, but they offer limited control on the number and the relative spacing between the energy-drop events. This paper shows that the combination of multiple slender elastic columns modulators, in parallel configurations, allows for the tailoring of the number and magnitude of the mode branch switching during the postbuckling response of the complete system. Experimental and numerical results are presented to validate the proposed concept.

Commentary by Dr. Valentin Fuster
2013;():V002T07A024. doi:10.1115/SMASIS2013-3217.

A novel class of two-stage electrical energy generators is presented for rotary machinery and rocking platforms in which the input speed is low and varies significantly, even reversing. Applications include wind mills, turbo-machinery for harvesting tidal flows, floating platforms and the like. Current technology using rotary generators requires gearing or similar mechanisms to increase the input speed to make the generation cycle efficient. Variable speed-control mechanisms are also usually needed to achieve high mechanical to electrical energy conversion efficiency. In this paper, electrical energy generators are presented that can efficiently operate at very low and highly variable and even intermittent and reversing speeds without requiring gearing or other speed control mechanisms. The generators are very simple in design and can significantly reduce complexity and cost, especially those pertaining to maintenance and servicing. In addition, these new generators can expand the application of energy harvesting to much slower input speeds than current technology allows.

The primary novelty of this technology is the two-stage harvesting system. In these energy harvesting systems, input mechanical energy from the environment such as wind or ocean waves is stored in a primary sub-system (stage) as potential energy. When the level of potential energy reaches a certain predetermined level, it is released into a secondary sub-system (stage). The secondary sub-system converts the stored mechanical energy into electrical energy. The secondary sub-system is preferably designed as vibrating mass-spring type energy harvester to achieve relatively high and nearly constant natural frequency and use piezoelectric or magnet and coil type generators to convert stored mechanical energy of vibration to electrical energy.

Commentary by Dr. Valentin Fuster
2013;():V002T07A025. doi:10.1115/SMASIS2013-3225.

Piezoelectric-based energy harvesting power sources that employ spring-mass vibrating systems have been employed with great success to harvest energy from various shock loading and/or vibration and oscillatory motions in numerous systems. In these systems, the external stimuli is used to store mechanical energy in the spring of a mass-spring unit which is attached to a piezoelectric element or a magnet and coil generator, and generate electrical energy as the vibrating mass-spring unit undergoes vibration and applies a cyclic load to the piezoelectric element. In this paper, the implementation of such energy harvesting power sources with a novel motion-doubling mechanism is presented. This novel force transmission method has two key advantages. Firstly, it provides the means to amplify the force applied to the piezoelectric element. Secondly, it provides the means of doubling the number of cycles of compressive forces applied to the piezoelectric elements during each cycle of vibration as compared to the direct mass-spring-piezoelectric generators that have been developed to date. The motion doubling and the resulting halving of the required number of cycles of vibration of the mass-spring unit for generating a certain amount of electrical energy has the effect of significantly increasing the mechanical to electrical energy conversion efficiency of the power source by significantly reducing structural damping losses in the spring element and by the increase in the level of force that is applied to the energy harvesting piezoelectric elements. The design and prototype fabrication of such an energy harvesting power sources is discussed.

Commentary by Dr. Valentin Fuster
2013;():V002T07A026. doi:10.1115/SMASIS2013-3228.

In this study, we have developed a sensor prototype for vibration acceleration monitoring driven by the authors’ proposed vibration energy harvester. It uses a commercial LTC3588 energy harvesting chip with capacitors and the piezo-bimorph cantilever-type energy harvester consists of the surface bonded two Macro-Fiber Composites. The power consumption of the acceleration sensor was typically 1mW, and the driving current was typically 400 microamperes. For vibration condition monitoring applications of industrial rotating machinery, we assumed that the typical casing or pedestal vibration amplitude of the rotating machinery was 0.71 mm/sec rms according to ISO standard. This low intensity excitation condition was the input for experimental evaluation of the developed sensor prototype. The sensor prototype was able to measure the vibration acceleration of approximately 17 seconds under the vibration input of 0.013G (RMS) at approximately 56Hz every two minutes. Approximately 12% of the input of vibration energy was used for driving the acceleration sensor. Therefore, estimated overall energy transfer efficiency was about 12%. The experimental results indicate the feasibility of the sensor prototype driven by piezocomposite vibration energy harvester.

Commentary by Dr. Valentin Fuster
2013;():V002T07A027. doi:10.1115/SMASIS2013-3247.

Previous studies on optimization of electromagnetic vibration energy harvesters assumed the radius and the height of a cylindrical construction volume to be fixed. We present optimization and comparison of three different types of electromagnetic vibration energy harvesters under constant volume conditions where the radius or the height can also be a design variable. The voltage and the power output are calculated for each architecture using finite element analysis. We found that different types of electromagnetic coupling architectures can be optimized with different shapes of the construction volumes.

Commentary by Dr. Valentin Fuster
2013;():V002T07A028. doi:10.1115/SMASIS2013-3297.

In this paper, a piezoelectric nanoelectromechanical system (NEMS) is fabricated using newly developed ultra-long (∼45μm) aligned barium titanate (BaTiO3) nanowire (NW) arrays that exhibit piezoelectric behavior for harvesting mechanical vibrational energy. The novel BaTiO3 NW NEMS is fabricated to have resonance at frequencies below 500 Hz for efficient energy harvesting since ambient mechanical vibrations typically exists in the 1 Hz to 1 kHz range. The maximum AC power harvested from the BaTiO3 NEMS is evaluated by impedance matching at resonant frequency. In addition, NEMS energy harvester comprised of seedless solution grown aligned ZnO NW arrays is also fabricated and direct vibration excitation experiments are performed to determine the peak AC power at optimal load resistor. Here, we clearly report the superior power harvesting capability from long ferroelectric BaTiO3 NW arrays than semiconducting ZnO NWs for the same electrode area when excited with the same sinusoidal base acceleration of 1g RMS at resonant frequency.

Commentary by Dr. Valentin Fuster
2013;():V002T07A029. doi:10.1115/SMASIS2013-3298.

This paper proposes a novel Tuned Magnetic Fluid Damper (TMFD) with energy harvesting capabilities to concurrently mitigate structural vibrations and harvest vibratory energy. The energy harvesting TMFD consists of a rectangular container carrying a magnetized ferrofluid and mounted on a vibrating structure. The ferrofluids geometric and material properties (height, surface area, magnetization) are tuned such the first modal frequency of the fluid column matches the first modal frequency of the structure. The one-to-one resonant interactions between the structure and the fluid column results in a direct energy transfer mechanism which mitigates the vibration of the structure by channeling energy to the ferrofluid. Consequently, the fluid undergoes a sloshing motion with large-amplitude surface waves that change the orientational order of the magnetic dipoles in the fluid. This creates a time-varying magnetic flux, which induces an electromotive force in a coil wound around the container. The electromotive force transforms a small part of the fluids kinetic energy into electricity by generating a current in the coil. Experimental studies performed on an actual TMFD prototype clearly demonstrate its vibration suppression potential and energy generation capabilities.

Commentary by Dr. Valentin Fuster

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