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Waste energy harvesting is a method of generating small amounts of energy, usually through vibrations or thermal energy. Macro-fiber Composites (MFCs) have been employed in energy harvesting applications utilizing the piezoelectric effect, however, energy harvesting using the pyroelectric effect in MFCs has not been thoroughly explored. This paper takes strides in investigating the energy generated using the pyroelectric effect with P1 and P2 MFCs using two different oscillating temperature rates at 5°C/min and 10°C/min. Numerical temperature data along with analytical temperature functions were used to model the pyroelectric effect and the result was compared to experimental tests. Depending on the size of the MFC, type, resistor used, and the temperature rate, the energy generated varies from 0.4 to 24 µJ for the P1 MFC, and 8 to 459 µJ for the P2 MFC. The maximum specific power was also estimated analytically, numerically, and experimentally. A resistor sweep was performed using the numerical model to calculate the optimal resistance that would provide the most energy. The resistor was in the Gigaohm (GΩ) to Teraohm (TΩ) range for the specified temperature profiles. The required resistance to generate the maximum energy decreased as the temperature rate and the size of the MFC increased. This was validated with experiments conducted at varying resistances. Because this is energy generated from the ambient environment, pyroelectric harvesting can be used to power devices without cost to the source. This form of harvesting can be used in any place where there is a natural thermal cycle (i.e. due to weather or machine giving off thermal energy).

The elastic instabilities associated with buckling in bistable structures have been harnessed toward energy-based and motion-based applications, with significant research toward energy harvesting and morphing. Often combined with smart materials, structural prototypes are designed with a single application in mind. Recently, a novel method of inducing bistability was proposed by bonding two piezoelectrically actuated macro fiber composites in a [Formula: see text] layup and releasing the voltage post cure to yield two cylindrically stable configurations. Since the macro fiber composites are simultaneously the actuator and host structure, the resulting efficiencies enable this bistable laminate to be multifunctional, with both broadband energy harvesting and snap-through morphing capabilities. This article experimentally characterizes the vibration-based energy harvesting performance of the laminate to enable morphing. Through frequency sweeps across the first two modes of both states, the laminate exhibits broadband cross-well dynamics that are exploited for improved power generation over linear resonant harvesters. Besides single-well oscillations, snap-throughs are observed in intermittencies and subharmonic, chaotic, and limit cycle oscillations. The maximum power output of each regime and their charge durations of an energy harvesting module are assessed. The laminate’s capabilities are then bridged by utilizing harvested energy in the charged module to initiate snap-through actuation.

Energy harvesting holds great potential to achieve long-lifespan self-powered operations of wireless sensor networks, wearable devices, and medical implants, and thus has attracted substantial interest from both academia and industry. This paper presents a comprehensive review of piezoelectric energy-harvesting techniques developed in the last decade. The piezoelectric effect has been widely adopted to convert mechanical energy to electricity, due to its high energy conversion efficiency, ease of implementation, and miniaturization. From the viewpoint of applications, we are most concerned about whether an energy harvester can generate sufficient power under a variable excitation. Therefore, here we concentrate on methodologies leading to high power output and broad operational bandwidth. Different designs, nonlinear methods, optimization techniques, and harvesting materials are reviewed and discussed in depth. Furthermore, we identify four promising applications: shoes, pacemakers, tire pressure monitoring systems, and bridge and building monitoring. We review new high-performance energy harvesters proposed for each application.

The capture of energy from vibration of mechanical systems has been extensively studied with the goal of providing power for various microelectromechanical systems. The traditional cantilever beam approach was used as a starting design for more complex, multiple-beam structures like zigzag or spiral geometries. This work presents the orthogonal spiral structure, an alternative compact periodic structure for reduced frequency energy harvesting. The proposed orthogonal spiral structure design is inspired by a combination of zigzag and Archimedean spiral geometries. The orthogonal spiral structure takes advantage of a simple cantilever beam-based design as with the zigzag, but includes the compact concentric-type design of an Archimedean spiral. First, the fundamental frequency is estimated using a lumped parameter model for the substrate beam and the results are compared with experimental results for two different sizes of orthogonal spiral structures. Then, the same model is updated to include a layer of piezoelectric material and used to identify the strain nodes along each beam obtained from the first mode shape. Finally, electromechanical modeling is developed allowing for the evaluation of the energy harvested from base excitations. The results show that the orthogonal spiral structure can be used as an alternative to current energy harvesting systems for micro scale applications.

Limited by the structure, the high-efficiency vibration energy harvesting and vibration suppression have always been a theoretical bottleneck and technical challenge in this field. The nonlinear design of the new vibration structure is an indispensable link in the development of vibration energy harvesting and vibration suppression technologies. Nonlinear technologies not only have the potential to improve the efficiency of the energy harvesters by increasing the useful frequency bandwidth and output power but also have the potential to improve the efficiency of vibration suppressors by reducing the transmission rate and transfer energy. Nonlinear vibration energy harvesting and vibration suppression technologies have been salient topics in the literature and have attracted widespread attention from researchers. The present work provides a comprehensive review on the recent advances in nonlinear vibration energy harvesting and vibration suppression technologies. In particular, the latest developments in multifunctional hybrid technologies are proposed. Various key aspects to improve the performance of nonlinear vibration energy harvesting and vibration suppression systems are discussed, including implementations and configuration designs, nonlinear dynamics mechanisms, various optimizations, multifunctional hybrid, application prospects, and future outlooks.

This paper presents a method for active vibration control of smart thin cantilever plates. For model formulation needed for controller design and simulations, finite difference technique is used on the cantilever plate response calculations. Piezoelectric patches are used on the plate, for which a neural network based control algorithm is formed and a neurocontroller is produced to calculate the required voltage to be applied on the actuator patch. The neurocontroller is trained and run with a Kalman Filter for controlling the structural response. The neurocontroller performance is assessed by comparing the controlled and uncontrolled structural responses when the plate is subjected to various excitations. It is shown that the acceleration response of the cantilever plate is suppressed considerably validating the efficacy of the neurocontroller and the success of the proposed methodology. Scopus

Nonlinear energy harvesters are very sensitive to ambient vibrations. If the excitation level is too low, their large-amplitude oscillations for high-energy voltage output cannot be obtained. A nonlinear tristable energy harvester has been previously proposed to achieve more effective broadband energy harvesting for low-level excitations. However, the sensitivity of its dynamic characteristics to the system parameters remains uninvestigated. Therefore, this paper theoretically analyzes the influence of the external load, the external excitation, the internal system parameters and the equilibrium positions on the dynamic responses of nonlinear tristable energy harvesters by using the harmonic balance method. In addition, numerical acceleration excitation thresholds and basins of attraction are provided to investigate the potential for energy harvesting performance enhancement using the suitable equilibrium positions, appropriate initial conditions or external disturbances, due to high-energy interwell oscillations in the multi-solution ranges. More importantly, experimental voltage responses of a given tristable energy harvester versus the external excitation frequency and amplitude verify the existence of experimental multi-solution ranges and the effectiveness of the theoretical analysis. It is also revealed that achieving high-energy interwell oscillations in the multi-solution ranges of tristable energy harvesters will be feasible for improving energy harvesting from low-level ambient excitations.

Sensors that provide critical information about jet engine performance are widely installed on static components but are rarely found on rotors because of their inaccessibility and extremely high rotation speeds. We present a new monitoring method, integrating energy harvesting technology with wireless sensors to achieve real-time self-powered engine monitoring. Energy harvesters, used to generate power from ambient vibration, are sustainable alternatives to batteries for achieving self-sustained long-term operation of electronic devices. By utilising structural nonlinearity, force amplification mechanism, and the piezoelectric effect, we show a 22.52-g energy harvester capable of high power output (78.87 mW), broad working bandwidth (22.5 Hz), and strong reliability (2100 RPM). Our approach breaks limitations from wired connections that are weighty and vulnerable to failures. We theoretically and experimentally analyse the nonlinear responses and demonstrate the harvester by constantly lighting 112 LEDs and a self-powered wireless sensor system in a jet engine. This work paves a new way for developing future monitoring systems for advanced jet engines and other rotating machinery applications.

The vibration based energy harvesting performance of a piezoelectrically generated bistable laminate consisting of only Macro Fiber Composites (MFC) is experimentally characterized. Conventionally, piezoelectric transducers are bonded onto thermally induced bistable composite laminates and exhibit broadband cross-well dynamics that are exploited for improved power generation over linear resonant harvesters. Recently, a novel method of inducing bistability was proposed by bonding two actuated MFCs in a [0 MFC ∕90 MFC ] T layup and releasing the voltage post cure to create in-plane residual stresses and yield two cylindrically stable configurations. Forward and backward frequency sweeps at multiple acceleration levels across the first two observed modes of the laminate’s two states are performed to identify all dynamic regimes and the corresponding voltages produced by each MFC. Besides single-well oscillations, snap throughs are observed in intermittencies, subharmonic, chaotic, and limit cycle oscillations across wide frequency ranges. Resistor sweeps are conducted for each regime to determine maximum power outputs, and single and multi-frequency performance metrics accounting for laminate volume, mass, input accelerations, and frequencies are evaluated for the laminate. A performance comparison with conventional bistable composite harvesters demonstrate the laminate’s viability for energy harvesting, allowing it to be multi-functional in combination with its snap through morphing capability.

Numerical and experimental investigations of nonlinear bistable energy harvesters (BEHs) with asymmetric potential functions are presented under various excitations for performance enhancement. Basin of attraction under harmonic excitation indicates that asymmetric potentials in BEHs have a negative effect on the power output. Therefore, a proper bias angle is introduced to the asymmetric potential BEHs for performance enhancement. Numerical and experimental results show that the power output is actually improved in a certain bias angle range under harmonic and random excitations. Furthermore, experiments under human motion excitation demonstrate that the asymmetric potential BEHs could perfectly combine with the asymmetric motion of lower-limb to improve the performance.

This paper presents a novel nonlinear piezoelectric energy harvesting system which consists of linear piezoelectric energy harvesters connected by linear springs. In principle, the presented nonlinear system can improve broadband energy harvesting efficiency where magnets are forbidden. The linear spring inevitably produces the nonlinear spring force on the connected harvesters, because of the geometrical relationship and the time-varying relative displacement between two adjacent harvesters. Therefore, the presented nonlinear system has strong nonlinear characteristics. A theoretical model of the presented nonlinear system is deduced, based on Euler-Bernoulli beam theory, Kirchhoff’s law, piezoelectric theory and the relevant geometrical relationship. The energy harvesting enhancement of the presented nonlinear system (when n = 2, 3) is numerically verified by comparing with its linear counterparts. In the case study, the output power area of the presented nonlinear system with two and three energy harvesters is 268.8% and 339.8% of their linear counterparts, respectively. In addition, the nonlinear dynamic response characteristics are analyzed via bifurcation diagrams, Poincare maps of the phase trajectory, and the spectrum of the output voltage.

Chaotic behavior presents intrinsic richness due to the existence of an infinity number of unstable periodic orbits (UPOs). The possibility of stabilizing these periodic patterns with a small amount of energy makes this kind of response interesting to various dynamical systems. Energy harvesting has as a goal the use of available mechanical energy by promoting a conversion into electrical energy. The combination of these two approaches may establish autonomous systems where available environmental mechanical energy can be employed for control purposes. Two different goals can be defined as priority, allowing a change between them: vibration reduction and energy harvesting enhancement. This work deals with the use of harvested energy to perform chaos control. Both control actuation and energy harvesting are induced employing piezoelectric materials, in a simultaneous way. A bistable piezomagnetoelastic structure subjected to harmonic excitations is investigated as a case study. Numerical simulations show situations where it is possible to perform chaos control using only the energy generated by the harvesting system.

Recently, piezo-aeroelastic energy harvesting has received greater attention. In the present study, a piezo-aeroelastic energy harvester using a nonlinear trailing-edge flap is proposed, and its nonlinear aeroelastic behaviors are investigated. The energy harvester is modeled using a piezo-aeroelastic model of a two-dimensional typical section airfoil with a trailing-edge flap (TEF). A piezo-aeroelastic analysis is carried out using RL and time-integration methods, and the results are verified with the experimental data. The linearizing method using a describing function is used for the frequency domain analysis of the nonlinear piezo-aeroelastic system. From the linear and nonlinear piezo-aeroelastic analysis, the limit cycle oscillation (LCO) characteristics of the proposed energy harvester with the nonlinear TEF are investigated in both the frequency and time domains. Finally, the authors discuss the air speed range for effective piezo-aeroelastic energy harvesting.

This work addresses the influence of nonlinearities in energy harvesting from a piezomagnetoelastic structure subjected to random vibrations. Nonlinear equations of motion that describe the electromechanical system are given along with theoretical simulations. The numerical analysis presents a comparison between the voltage provided from a linear, nonlinear bistable and nonlinear monostable systems due to random vibration. Experimental performance of the generator exhibits qualitative agreement with the theory, showing an enhancement of piezoelectric power generation in a bistable system when it vibrates around both stable equilibrium points. A relationship between variations in the excitation and a bistable system response is established from numerical simulations, defining a region of enhanced power generation when compared to the linear and nonlinear monostable cases.

This study is at attempt to explore the nonlinear behavior of bistable composite laminates for vibration energy harvesting. Asymmetric four-ply [0/90/0/90] carbon-fiber plate with two cylindrical stable equilibria supported at its center and free at all boundaries is used for the experimental testing. Macro-fiber composite (MFC) patches are attached to the plate to transform the mechanical vibration energy into electrical energy. The mechanical bistable property of the plate makes it possible to snap from one stable equilibrium state to the other. This snapthrough motion is highly nonlinear and associated with large-amplitude vibrations. The experimental tests aim at exploiting the nonlinearity due to the snapthrough motion to enhance the energy extraction. First, the resonant frequencies and damping of the plate are identified. A primary-resonance excitations of the first mode are carried out using two schemes: amplitude sweep and frequency sweep. In the first case, amplitude sweep, the excitation frequency is kept fixed at the resonant frequency and the amplitude of excitation is increased. The time history and FFT of the response as well as the output voltage are measured and reported. In the second case, frequency sweep, the excitation frequency is varied around the resonant frequency while the excitation amplitude is kept fixed. In both cases, the response shows a small-amplitude single-well vibrations at low excitation amplitudes and chaotic and periodic snapthrough motion as the amplitude and frequency of excitation are varied. The snapthrough motion has been found to greatly enhance the energy extraction capability. This study can serve as a motive for more testing and modeling efforts in order to understand the complex nonlinear behavior of bistable composite laminates and exploit it for vibration energy harvesting.

The research presented in this paper focuses on a unique multifunctional structural design that not only absorbs vibration at desired frequency bands, but also extracts significant amounts of electrical energy. This is accomplished by first designing an array of low-frequency resonators to be integrated into a larger host structure. This array of resonators can contribute not only to static requirements, e.g., stiffness, strength, mass, etc., of the host structure but the array also functions as a distributed system of passive vibration absorbers. Structures having these distributed vibration absorber systems are known as metastructures. Here, the authors present a unique absorber design referred to as a zigzag beam, which can have a natural frequency an order of magnitude lower than that of a basic cantilever beam of the same scale. It will be shown that the zigzag beams can be designed with an added layer of piezoelectric material, which allows them to harvest significant amounts of electrical power as they suppress vibration of the host structure. This paper includes details of the fully-coupled electromechanical analytical and numerical models for energy harvesting metastructures. Experimental results used to validate the proposed modeling methods will be discussed. Lastly, results of a multi-objective design optimization will be presented and discussed. Results of the optimization study were able to show that allowing only an 82 % increase in the host structure vibration could yield more than a 1500 % increase in total power output. Other results show that the power output (or absorber motion) could be increased 241% without increasing host structure vibrations due to multiple design solutions existing at fixed host structure vibration levels.

Research involving energy harvesters to power systems are often carried out in a laboratory setting where vibration excitations are created using shakers. These excitations can be tuned to the natural frequency of the harvester to achieve the highest power output possible for the harvester design. Adapting these designs for use in real world applications introduces many additional layers of complexity. These added complications come in various forms including different input vibration and acceleration profiles, sensor energy requirements, and space constraints. Existing optimization for application-based research is limited to one set of constraints and cannot be applied to different cases.

Metastructures are known to provide considerable vibration attenuation for mechanical systems. With the optimization of the internal geometry of metastructures, the suppression performance of the host structure increases. While the zigzag inserts have been shown to be efficient for vibration attenuation, the geometric properties of the inserts affect the suppression performance in a complex manner when attached to the host structure. This paper presents a genetic algorithm based optimization study conducted to come up with the most efficient geometric properties of the zigzag inserts. The inserts studied in this paper are simply cantilever zigzag structures with a mass attached to the unsupported tips. Numerical simulations are run to show the efficiency of the optimization process. Scopus

This paper proposes the theoretical model and experimental investigations of a broadband piezoelectric based vibration energy harvester with a triple-well potential induced by a magnetic field. The mathematical model is derived from the energy method to describe the response characteristics of nonlinear tristable energy generators. The parameters of the linear energy harvesting system without magnetic force actuation are obtained through intelligent optimization of the minimum error between numerical simulations and experimental responses. The equivalent nonlinear restoring force of the tristable oscillator is experimentally identified as a high order polynomial. Numerical simulations and experiments are performed at different harmonic excitation levels ranging from 1 to 20 Hz. The results verify that the identified electromechanical model can describe the dynamic characteristics of broadband tristable energy harvesters. Furthermore, in comparison to bistable nonlinear energy oscillators with deeper potential well, the tristable arrangement passes easily through potential wells for generating higher energy output over a wider range of frequency.

Piezoelectric materials play a significant role in harvesting ambient vibration energy. Due to their inherent characteristics and electromechanical interaction, the system damping for piezoelectric energy harvesting can be adequately characterized by fractional calculus. This paper introduces the fractional model for magnetically coupling broadband energy harvesters under low-frequency excitation and investigates their nonlinear dynamic characteristics. The effects of fractional-order damping, excitation amplitude, and frequency on dynamic behaviors are proposed using the phase trajectory, power spectrum, Poincare map, and bifurcation diagram. The numerical analysis shows that the fractionally damped energy harvesting system exhibits chaos, periodic motion, chaos and periodic motion in turn when the fractional order changes from 0.2 to 1.5. The period doubling route to chaos and the inverse period doubling route from chaos to periodic motion can be clearly observed. It is also demonstrated numerically and experimentally that the magnetically coupling piezoelectric energy harvester possesses the usable frequency bandwidth over a wide range of low-frequency excitation. Both high-energy chaotic attractors and large-amplitude periodic response with inter-well oscillators dominate these broadband energy harvesting.

The exploitation of nonlinear behavior in vibration-based energy harvesters has received much attention over the last decade. One key motivation is that the presence of nonlinearities can potentially increase the bandwidth over which the excitation is amplified and therefore the efficiency of the device. In the literature, references to resonating energy harvesters featuring nonlinear oscillators are common. In the majority of the reported studies, the harvester powers purely resistive loads. Given the complex behavior of nonlinear energy harvesters, it is difficult to identify the optimum load for this kind of device. In this paper the aim is to find the optimal load for a nonlinear energy harvester in the case of purely resistive loads. This work considers the analysis of a nonlinear energy harvester with hardening compliance and electromagnetic transduction under the assumption of negligible inductance. It also introduces a methodology based on numerical continuation which can be used to find the optimum load for a fixed sinusoidal excitation.

Materials like the Macro-fiber Composite (MFC) are employed in energy harvesting applications utilizing the piezoelectric effect. However, energy harvesting using the pyroelectric effect in MFCs is an unexplored topic. This paper takes strides in understanding the thermal micromechanical interactions that MFCs experience due to this effect and leads to a better understanding of how MFCs behave in thermal environments. In this work, the pyroelectric coefficient (primary and secondary) are estimated for P1 and P2 Macro-fiber Composites (MFCs) using micromechanical modeling and experimental techniques. The coefficient of thermal expansion (CTE) is estimated using micromechanical theory for both MFC types which is consequently used in the modeling of the pyroelectric coefficient. Secant based moduli are used to better approximate the properties of components of MFCs in the regime of linear elasticity. Two experiments are conducted to measure the pyroelectric coefficient under different boundary conditions. In the first experiment, the thermal expansion of the MFC is constrained in a Kevlar envelope, while in the second experiment, the MFC is epoxied onto a metal shim allowing restricted deformations. Thermal experiments were conducted in an altitude chamber where the resulting average pyroelectric coefficient is calculated for both experiments.

The continuing need for reduced power requirements for small electronic components, such as wireless sensor networks, has prompted renewed interest in recent years for energy harvesting technologies capable of capturing energy from ambient vibrations. A particular focus has been placed on piezoelectric materials and devices due to the simplicity of the mechanical to electrical energy conversion and their high strain energy densities compared to electrostatic and electromagnetic equivalents. In this paper an arrangement of piezoelectric layers attached to a bistable asymmetric laminate is investigated experimentally to understand the dynamic response of the structure and power generation characteristics. The inherent bistability of the underlying structure is exploited for energy harvesting since a transition from one stable configuration to another, or "snap-through", is used to repeatedly strain the surface bonded piezoelectric and generate electrical energy. This approach has been shown to exhibit high levels of power extraction over a wide range of vibrational frequencies. Using high speed digital image correlation, a variety of dynamic modes of oscillation are identified in the harvester. The sensitivity of such modes to changes in vibration frequency and amplitude are investigated. Power outputs are measured for repeatable snap-through events of the device and are correlated with the measured modes of oscillation. The typical power generated is approximately 3.2 mW, comparing well with the needs of typical wireless senor node applications.

In the present study, a piezo-aeroelastic energy harvester using nonlinear aeroelastic behaviors is proposed, and their characteristics and performance are investigated. The energy harvester is modeled by a two-dimensional typical section airfoil. The nondimensional parameters of the harvester are introduced, and the nondimensional piezo-aeroelastic equations are formulated. For the piezo-aeroelastic analysis, the root-locus method and time-integration method are used, and the present method is verified with experimental and analytical results. The iterative method is introduced to calculate the frequency response functions of a nonlinear piezo-aeroelastic energy harvester. The aeroelastic characteristics of a linear piezo-aeroelastic energy harvester and the effects of parameters are investigated. The results show that the linear piezo-aeroelastic energy harvester can be used to generate electricity only at the vicinity of flutter speed. It is assumed that the nonlinear piezo-aeroelastic energy harvester has free play and cubic hardening in pitch. For free play, nonlinear aeroelastic results show that stable limit cycle oscillations are observed in the wide range of air speed below flutter speed when the frequency ratio is 1.3, and unstable limit cycle oscillations are observed at air speeds over flutter speed when the frequency ratio is 0.3. For cubic hardening, unstable limit cycle oscillations are observed at air speeds below flutter speed when the frequency ratio is 0.3, and stable limit cycle oscillations are observed at air speeds over flutter speed when the frequency ratio is 1.3. Finally, the authors discussed how to use these aeroelastic responses for piezo-aeroelastic energy harvesting.

This paper experimentally examines a multifunctional gust alleviation system and holds promise for improving small unmanned aerial vehicles performance in wind gusts. The designed multifunctional wing spar is able to harvest energy itself from the normal vibrations during flight. If the wing experiences any strong wind gust, it will provide vibration control to maintain its stability. The proposed wing spar carries on the functions of energy harvesting, strain sensing, and gust alleviation via piezoelectric materials. A closed form electromechanical cantilever multifunctional beam model is developed, which captures the basics of piezoelectric constitute equations using Euler-Lagrange equations. An enhanced two mode reduced energy control (REC) law is developed to saturate a positive strain feedback (PSF) control law, and therefore decrease energy consumption but maintains the same gust alleviation performance. An equivalent circuit model is also developed based on the distributed parameter method to represent a multifunctional gust alleviation system using harvested energy. Experimental results show that compared to conventional PSF control law, the REC decreases voltage supply from ±20 to ±4 V, uses 76% less energy whereas maintaining the same performance. Experimental results also show that it is feasible to alleviate wind gust disturbance using harvested power from ambient vibrations, but requires the harvesting time to be 0.42 times longer than the wind gust duration.

The long composite blades on large wind turbines experience tremendous stresses while in operation. There is an interest in implementing structural health monitoring (SHM) systems inside wind turbine blades to alert maintenance teams of damage before serious component failure occurs. This paper proposes using an energy harvesting device inside the blade of a horizontal axis wind turbine to power a SHM system. The harvester is a linear induction energy harvester placed radially along the length of the blade. The rotation of the blade causes a magnet to slide along a tube as the blade axis changes relative to the direction of gravity. The magnet induces a voltage in a coil around the tube, and this voltage powers the SHM system. This paper begins by discussing motivation for this project. Next, a harvester model is developed, which encompasses the mechanics of the magnet, the interaction between the magnet and the coil, and the current in the electrical circuit. A free fall test verifies the electromechanical coupling model, and a rotating test examines the power output of a prototype harvester. Copyright © 2013 John Wiley & Sons, Ltd.

A nonlinear piezoelectric rotary transducer is developed that makes compact low speed wind generators realizable. Compact wind generators provide power to sensor nodes in remote or hard to reach locations. Since the locations of the sensor nodes are not optimized in terms of wind speed, the compact wind generators should be able to produce power from low speed wind. At smaller scales piezoelectric transduction becomes more effective than electromagnetic transduction. Therefore one way of realizing the compact wind turbines is by replacing the electromagnetic generator with a piezoelectric transducer. This work presents a novel piezoelectric transducer where the rotation of the blades results in large oscillations of piezoelectric beams. The piezoelectric bimorphs are made bi-stable by incorporation of repelling magnetic force. The Magnetic force is due to interaction of permanent magnets at the tip of the beams with permanent magnets rotating with the blades. Since the magnetic force changes with blade rotation, the dynamics of the beams changes in time and the system is thus parametrically excited. Two configurations are presented one called tangential configuration and the other is radial configuration. An 80 mm × 80 mm × 175 mm nonlinear piezoelectric wind generator can generate milliwatts of power from wind as slow as 2 ms −1 . The proposed compact wind generators are experimentally investigated in two steps. First the piezoelectric transducer is examined through constant rotational speed tests. Second wind tunnel experiments are performed to characterize the entire wind generator. An analytical model is developed for the piezoelectric rotational transducer. The model is verified with the experimental results. The nonlinear phenomena captured by the experimental investigations are explained using the analytical model. The model is also used for more case studies identifying specifically the effect of parametric excitations.

This article examines the concept and design of a multifunctional composite sandwich structure for simultaneous energy harvesting and vibration control. The intention is to design a composite wing spar for a small unmanned aerial vehicle which is able to harvest energy itself from ambient vibrations during normal flight along with available sunlight. If the wing experiences any strong wind gust, it will sense the increased vibration levels and provide vibration control to maintain its stability. The proposed multifunctional composite wing spar integrates a flexible solar cell array, piezoelectric wafers, a thin film battery, and an electronic module into a composite sandwich structure. The piezoelectric wafers act as sensors, actuators, and harvesters. The basic design factors are discussed for a beam-like multifunctional wing spar with energy harvesting, strain sensing, and self-controlling functions. The configurations, locations, and operating modes of piezoelectric transducers are also discussed for optimal power generation. The equivalent electromechanical representations of a multifunctional wing spar is derived theoretically and simulated numerically. Special attention is given to the self-contained gust alleviation with the goal of using available energy harvested from ambient vibrations. A reduced energy control law is implemented to reduce the actuation energy and the dissipated heat. This law integrates saturation control with a positive strain feedback controller and is represented by a positive feedback operation amplifier and a voltage buffer operation amplifier for each mode. This study builds off of our previous research and holds promise for improving unmanned aerial vehicle performance in wind gusts. Here, we also include, but not use, a flexible solar panel in our modeling.

This article presents a summary of passive, semipassive, semiactive, and active control methods for schemes using harvested energy as the main source of energy to suppress vibrations via piezoelectric materials. This concept grew out of the fact that energy dissipation effects resulting from energy harvesting can cause structural damping. First, the existing equivalent electromechanical modeling methods are reviewed for vibration-based energy harvesters using piezoelectric transducers. Modeling of base excitation cantilever beam ranges from lumped to distributed parameter formulations. The commonly used electrical power conditioning circuits and their optimization are also summarized and discussed. The energy dissipation from harvesting induces structural damping, and this leads to the concept of purely passive shunt damping. This article reviews the literature on vibration control laws along the lines of purely passive, semipassive, semiactive, and active control. The classification of pervious results is built on whether external power is supplied to the piezoelectric transducers. The focus is placed on recent articles investigating semipassive and semiactive control strategies derived from synchronized switching damping. However, whether or not the harvested energy is large enough to satisfy a vibration suppression requirement has become an important topic of research but has not yet specifically been addressed in previous studies. Hence, this survey also reviews the possible control methods aiming for less control energy consumption and addresses the potential application for simultaneous vibration control and energy harvesting.

This paper presents an electromechanical comparison of the transduction capabilities of a clamped-free Macro-Fiber Composite (MFC) actuated unimorph to other unimorphs employing monolithic piezoceramic devices. Four cantilevered unimorph beams, employing PSI PZT-5A, PSI PZT-5H, MIDE QP10N and MFC 8528-P1 type devices, are analyzed in the comparison. The unimorphs are evaluated for their actuation performance via tip displacement induced with harmonic voltage excitation, energy harvesting via electrical power output on a resistive shunt induced by harmonic base acceleration and linear feedback control effectiveness with the application of a Positive Position Feedback controller. The constitutive nonlinearities arising from large strain and electric field amplitudes are identified and briefly discussed. The MFC 8528-P1 type unimorph showed the highest mass-normalized actuation authority and the lowest energy harvesting capability.

DOI: 10.2514/1.C031542 This paper presents the investigation of a multifunctional energy harvesting and energy-storage wing spar for unmanned aerial vehicles. Multifunctional material systems combine several functionalities into a single device in order to increase performance while limiting mass and volume. Multifunctional energy harvesting can be used to provide power to remote low-power sensors on unmanned aerial vehicles, where the added weight or volume of conventional harvesting designs can hinder flight performance. In this paper, a prototype self-charging wing spar containing embedded piezoelectric and battery elements is modeled, fabricated, and tested to evaluate its energy harvesting and storage performance. A coupled electromechanical model based on the assumed modes method is developedtopredictthevibrationresponseandvoltageresponseofacantileveredwingsparexcitedunderharmonic base excitation. Experiments are performed on a representative self-charging wing spar, and the results are used to verify the electromechanical model. The power-generation performance of the self-charging wing spar is investigatedindetailforharmonicexcitationinclamped–freeboundaryconditions.Experimentsarealsoconducted to demonstrate the ability of the wing spar to simultaneously harvest and store electrical energy in a multifunctional manner.Itisshownthat,foraninputbaseaccelerationlevelof0:25 gat28.4Hzatthebaseofthestructure,1.5mW of regulated dc power isdelivered from the piezoelectric layers to the thin-film battery, resulting in a stored capacity of 0.362 mAh in 1 h.

Nonlinear piezoelectric effects in flexural energy harvesters have recently been demonstrated for drive amplitudes well within the scope of anticipated vibration environments for power generation. In addition to strong softening effects, steady-state oscillations are highly damped as well. Nonlinear fluid damping was previously employed to successfully model drive dependent decreases in frequency response due to the high-velocity oscillations, but this article instead harmonizes with a body of literature concerning weakly excited piezoelectric actuators by modeling nonlinear damping with nonconservative piezoelectric constitutive relations. Thus, material damping is presumed dominant over losses due to fluid-structure interactions. Cantilevers consisted of lead zirconate titanate (PZT)-5A and PZT-5H are studied, and the addition of successively larger proof masses is shown to precipitate nonlinear resonances at much lower base excitation thresholds while increasing the influence of higher-order nonlinearities. Parameter identification results using a multiple scales perturbation solution suggest that empirical trends are primarily due to higher-order elastic and dissipation nonlinearities and that modeling linear electromechanical coupling is sufficient. This article concludes with the guidelines for which utilization of a nonlinear model is preferred.

A unified approximation method is derived to illustrate the effect of electro-mechanical coupling on vibration-based energy harvesting systems caused by variations in damping ratio and excitation frequency of the mechanical subsystem. Vibrational energy harvesters are electro-mechanical systems that generate power from the ambient oscillations. Typically vibration-based energy harvesters employ a mechanical subsystem tuned to resonate with ambient oscillations. The piezoelectric or electromagnetic coupling mechanisms utilized in energy harvesters, transfers some energy from the mechanical subsystem and converts it to an electric energy. Recently the focus of energy harvesting community has shifted toward nonlinear energy harvesters that are less sensitive to the frequency of ambient vibrations. We consider the general class of hybrid energy harvesters that use both piezoelectric and electromagnetic energy harvesting mechanisms. Through using perturbation methods for low amplitude oscillations and numerical integration for large amplitude vibrations we establish a unified approximation method for linear, softly nonlinear, and bi-stable nonlinear energy harvesters. The method quantifies equivalent changes in damping and excitation frequency of the mechanical subsystem that resembles the backward coupling from energy harvesting. We investigate a novel nonlinear hybrid energy harvester as a case study of the proposed method. The approximation method is accurate, provides an intuitive explanation for backward coupling effects and in some cases reduces the computational efforts by an order of magnitude.

An analytical electromechanical model is proposed to predict the deflection, voltage, and the power output of a proposed low-frequency micro-harvesting structure. The high natural frequencies of the existing designs of micro-scale vibrational energy harvesters are serious drawbacks. A zigzag design is proposed to overcome this limitation. First, the natural frequencies and the mode shapes of the zigzag structure are calculated. The piezoelectric direct and reverse effect equations, together with the electrical equations, are used to relate the voltage output of the structure to the base vibrations magnitude and frequency. The closed-form solution of the continuous electromechanical vibrations gives the power output as a function of base acceleration spectrum. The usefulness of the design is proved by the significant increase of the power output from the same base accelerations, providing a method of designing a micro-scale harvester with low natural frequency. The optimal mechanical and electrical conditions for power generation are investigated through the case studies.

In this work, the pyroelectric coefficient for macro fiber composites (MFCs) was characterized by first modeling the secondary pyroelectric coefficient using material properties of MFCs, and then experimentally computing the total pyroelectric coefficient using two separate thermal chambers. The computed total secondary pyroelectric coefficient was 29.88 μC m−2 K−1. The primary pyroelectric coefficient will be higher due to the primary effect having a more dominate influence in ferroelectric materials. The sum of the primary and secondary effects is the total pyroelectric coefficient. The MFC was tested in thermal chambers at NASA Langley and at University of Michigan where the temperature was ramped to 70 °C, as well as thermally cycled between 40 °C and 100 °C. The P2 MFC type yielded a higher pyroelectric coefficient than the P1 type at about −343 versus −82 μC m−2 K−1. The higher the pyroelectric coefficient is, the more energy it produces for given temperature fluctuations with time. This leads to future work in energy harvesting using the pyroelectric effect and further advancing potential novel applications using MFCs.

The future in terms of autonomous devices is about to experience an important breakthrough because of the development of energy-harvesting systems. This paper presents a new vibration energy-harvesting electrical interface for optimizing the power extracted from piezoelectric elements. Based on piezoelectric energy-harvesting properties, the proposed circuit allows an optimization of the extracted energy independently from the structure's parameters and without any tuning required. Contrary to classical converter topologies (for instance, step-down or buck-boost), the proposed architecture does not require large inductors, allowing a high-integration potential, while requiring a very little power consumption.

The recent proliferation of microscale devices has raised the issue of energy harvesting for replacing batteries that present maintenance and recycling problems. Particularly, piezoelectric seismic microgenerators offer the advantages of easy maintenance and high power output, but are very sensitive to frequency drifts that can dramatically decrease their performance. The purpose of the present article is to expose a technique to ensure that the harvester resonance frequency matches the base motion frequency, without any external intervention. The principles of the proposed method rely on ultralow-cost frequency sensing combined with an energy-efficient stiffness tuning, through the use of an additional actuator. Experimental results carried out to validate the model show that such an approach permits increasing the effective bandwidth of the structure by a factor of 4 in terms of mechanical vibrations and having a 100% frequency band gain in terms of total power output of the device (i.e., taking into account the energy spent by the actuation). The total energy produced by the harvesting device, taking into account the actuation cost, is discussed as well.

A two-stage power conditioning circuit consisting of an AC-DC converter followed by a DC-DC converter is proposed for a vibration-based energy harvesting system. The power conditioning circuit intends to maximize the amount of power extracted from a piezoelectric energy harvester by matching the source impedance with the circuit by adaptively adjusting the duty cycle. An equivalent electrical circuit representation derived from a distributed-parameter piezoelectric energy harvester model is adapted to enable the impedance matching method proposed here. For a given piezoelectric energy harvester, there is a theoretical maximum power output that is determined by the mechanical damping, base acceleration, and the effective mass of the harvester structure under base excitation. Experimental results are given to validate the effectiveness of the proposed resistive impedance matching circuit around the first resonance frequency of a cantilevered piezoelectric energy harvester.

Advances in low-power electronics and in energy harvesting technologies have enabled the conception of truly self-powered devices. Nevertheless, most studies rely on steady-state assumptions, which are rarely available in real environments. This article exposes, as a first step, a study of the transient stage of vibration energy harvesting systems initially at rest both mechanically and electrically (null initial displacement and voltages), when the harvesting device is submitted to a time-limited sine force at its resonance frequency. A particular focus will be placed on the total energy harvested as well as on the time of harvesting, allowing a better understanding of the dynamics of harvesting processes for systems subjected to time-limited excitations.

The optimization of power acquired from a piezoelectric vibration-based energy harvester which utilizes a harvesting circuit employing an inductor and a resistive load is described. The optimization problem is formulated as a nonlinear program wherein the Karush–Kuhn–Tucker (KKT) conditions are stated and the resulting cases are treated. In the first part of the manuscript, the case of a purely resistive circuit is analyzed. While this configuration has received considerable attention in the literature, previous efforts have neglected the effect of damping on the optimal parameters. Here, we explore the impact of damping on power optimality and illustrate its quantitative and qualitative effects. Further, we analyze the effect of electromechanical coupling demonstrating that the harvested power decreases beyond an optimal coupling coefficient. This result challenges previous literature suggesting that higher coupling coefficients always culminate in more efficient energy harvesters. In the second part of this work, the effect of adding an inductor to the circuit is examined. It is demonstrated that the addition of the inductor provides substantial improvement to the performance of the energy harvesting device. It is also shown that within realistic values of the coupling coefficient, the optimal harvested power is independent of the coupling coefficient; a result that supports previous findings for the purely resistive circuit.

The development of a digital signal processor based prototype is described in relation to continuing efforts for realizing a fully self-contained active sensor system utilizing impedance-based structural health monitoring. The impedance method utilizes a piezoelectric material bonded to the structure under observation to act as both an actuator and sensor. By monitoring the electrical impedance of the piezoelectric material, insights into the health of the structured can be inferred. The active sensing system detailed in this paper interrogates a structure utilizing a self-sensing actuator and a low cost impedance method. Here, all the data processing, storage, and analysis is performed at the sensor location. A wireless transmitter is used to communicate the current status of the structure. With this new low cost, field deployable impedance analyzer, reliance on traditional expensive, bulky, and power consuming impedance analyzers is no longer necessary. A complete power analysis of the prototype is performed to determine the validity of power harvesting being utilized for self-containment of the hardware. Experimental validation of the prototype on a representative structure is also performed and compared to traditional methods of damage detection.

Cantilevered beams with piezoceramic (PZT) layers are the most commonly investigated type of vibration energy harvesters. A frequently used modeling approach is the single-degree-of-freedom (SDOF) modeling of the harvester beam as it allows simple expressions for the electrical outputs. In the literature, since the base excitation on the harvester beam is assumed to be harmonic, the well known SDOF relation is employed for mathematical modeling. In this study, it is shown that the commonly accepted SDOF harmonic base excitation relation may yield highly inaccurate results for predicting the motion of cantilevered beams and bars. First, the response of a cantilevered Euler—Bernoulli beam to general base excitation given in terms of translation and small rotation is reviewed where more sophisticated damping models are considered. Then, the error in the SDOF model is shown and correction factors are derived for improving the SDOF harmonic base excitation model both for transverse and longitudinal vibrations. The formal way of treating the components of mechanical damping is also discussed. After deriving simple expressions for the electrical outputs of the PZT in open-circuit conditions, relevance of the electrical outputs to vibration mode shapes and the electrode locations is investigated and the issue of strain nodes is addressed.

Autonomous, wireless structural health monitoring is one of the key goals of the damage monitoring industry. One of the main roadblocks to achieving autonomous sensing is removing all wiring to and from the sensor. Removing external connections requires that the sensor have its own power source in order to be able to broadcast/telemetry information. Furthermore if the sensor is to be autonomous in any way, it must contain some sort of computing and requires additional power to run computational algorithms. The obvious choice for wireless power is a battery. However, batteries often need periodical replacement. The work presented here focuses on using ambient energy to power an autonomous sensor system and recharge batteries and capacitors used to run an active sensing system. In particular, we examine methods of harvesting energy to run sensor systems from ambient vibration energy using piezoelectric elements.

Bistable composite laminates have received a considerable attention due to their fabulous behavior and potential for morphing and energy harvesting. A bistable or multistable laminate is a type of composite structure that exhibits multiple stable static configurations. The characterization of unsymmetric fiber-reinforced laminated composite plates as a bistable structure is well established and quantitatively determined after about 30 years of research. As predicting cured shapes of unsymmetric composite laminates became well identified, attention was directed to the design of these structures for morphing applications. Bistable composite laminates have attracted researchers as a morphing structure because a bistable structure settles at one of its equilibrium positions without demanding continuous power to remain there. If the structure is triggered to leave an equilibrium position, it will snap or jump to the other equilibrium position. The snapthrough response is highly geometrically nonlinear. With the increased demand for broadband vibration energy harvesters, bistable composite laminates, which are able to gain large-amplitude vibrations in snapthrough motion, have recently attracted attention. This paper aims to summarize, review, and assess references and findings concerned with the response of bistable composite laminates for morphing and energy harvesting to date. It also highlights the remaining challenges and possible future research work as research in bistable composites transitions from phenomena to application.

This paper presents a linear-spring coupled nonlinear energy harvesting system, which contains linear piezoelectric energy harvesters coupled by linear springs. Although every element of the system is linear, the system will present nonlinear characteristics when it is subjected to excitations because of the geometric nonlinearity induced by coupled motions. Three non-uniform cross-section linear harvesters with the same total length and the different thickness are selected to form the proposed system. Based on Euler-Bernoulli beam assumptions and the geometrical relationship among each element, a detailed modeling process of the proposed system is presented. In order to verify the broadband characteristics, the comparison of the proposed system and its linear counterparts is provided. Under harmonic excitations, the proposed system has much better energy harvesting capacity compared with its linear counterparts. What’s more, the energy harvesting performance of the proposed system is a little better than its linear counterparts under random excitations. The results demonstrate that the advantage of the proposed system is enhanced along with increased excitation level. In addition, such non-magnetic nonlinear energy harvesting system can be used in the areas where magnets are forbidden, such as inside the human body.Copyright © 2015 by ASME

Research presented in this paper focuses on the experimental and theoretical analysis of a compact, nonlinear, broadband energy harvesting device. Cantilevered structure zigzag beams have been shown to have natural frequencies orders of magnitudes lower than traditional cantilever beam geometries of the same size. Literature has also demonstrated that a cantilever beam harvester design combined with a magnetic field introduces nonlinearities in the response which can increase bandwidth of the device. Current energy harvester designs are relatively large in size, are most efficient at high frequencies, or only useful for narrowband linear operation. The proposed research introduces a zigzag geometry beam used in conjunction with a magnetic field to create a compact device capable of low frequency broadband energy harvesting. Experimental results are shown comparing both the linear and nonlinear energy harvesting capabilities of the zigzag structures. Experimental results are the focus of this paper, however, analytical expressions for the fundamental mode shape, natural frequency, and electromechanical coupling are presented for the linear lumped parameter system. A physics based magnetic force model for the nonlinear system is also proposed.

With the recent advances in wireless technology and low power electronics the idea of capturing the ambient energy surrounding a system and using it to provide electrical power to devices that do not rely on external power supplies has received a significant amount of attention. Much of this attention has been aimed at the use of piezoelectric materials to capture ambient vibrations. However, the energy generated by such materials is far too small to directly power most of the electronic devices. Therefore, in the present study a Seebeck heat pump is used to convert the ambient thermal gradient generated by solar radiation and waste heat into usable electrical energy. To increase the amount of thermal radiation captured by the power harvesting device, the hot side of the thermoelectric generator is placed in a small greenhouse, while the cold side is secured against a thermal sink, such as a highway bridge. The power generated by the thermoelectric device is shown to be substantially greater than that produced by piezoelectric materials and the ability to recharge a discharged battery is demonstrated. This research focuses on the use of thermal electric generators in a passive configuration where only conduction is used to remove heat from the device. The majority of previous studies have implemented convective heat transfer to increase power output and have only reported gross energy production. The results show that thermal electric materials when used in a passive fashion can form effective power sources with the ability to quickly recharge discharged batteries.

The use of piezoelectric materials for power harvesting has gained significant interest over the past few years. The majority of research on this subject has sought to quantify the amount of energy generated in power harvesting applications, or to develop methods of improving the amount of energy generated. Usually, a monolithic PZT material with a traditional electrode pattern and poled through its thickness is used in power harvesting research projects. In recent years, however, several companies and research institutions have begun to develop and market a broad range of piezoelectric composite sensor/actuator packages, each conceived for specific operational advantages and characteristics. Commonly, these devices are employed in control and vibration suppression applications, and their potential for use in power harvesting systems remains largely unknown. Two frequently implemented design techniques for improving the performance of such actuators are the use of interdigitated electrodes and piezofibers. This paper seeks to experimentally quantify the differences in power harvesting application performance between several of these new actuators and to identify the reasons for their relative performance characteristics. A special focus on the structural and compositional differences between each actuator is incorporated in the discussion of the effectiveness of each actuator as power harvesting devices.