No description available.

This work is centered on low-frequency and high-frequency multiphysics problems of piezoelectric structures submerged in a quiescent fluid domain for the applications of vibration energy harvesting, biomimetic actuation, and contactless acoustic energy transfer. In the first part of this research, Macro-Fiber Composite (MFC)-based piezoelectric structures are employed for underwater mechanical base excitation and electrical biomimetic actuation in bending mode at low frequencies (the fundamental underwater bending resonance being in the infrasonic frequency range). The MFC technology (fiber-based piezoelectric composites with interdigitated electrodes) exploits the effective 33-mode of piezoelectricity, and strikes a balance between structural deformation and force levels for actuation to use in underwater locomotion, in addition to offering high power density for energy harvesting to enable battery-less aquatic sensors. Following in-air electroelastic composite model development, the fundamental research problem is to establish semi-analytical models that can predict the underwater dynamics of thin MFC cantilevers for different length-to-width aspect ratios. In-air analytical electroelastic dynamics of MFCs is therefore coupled with added mass and nonlinear hydrodynamic damping effects of fluid to describe the underwater electrohydroelastic dynamics in harvesting and actuation. To this end, passive plates of different aspect ratios are tested to extract and explore the repeatability of the inertia and drag coefficients in Morison’s equation. The focus is placed on the first two bending modes in this semi-empirical approach. In particular, electrode segmentation is studied for performance enhancement in the second bending mode. Additionally, nonlinear dependence of the output power density to aspect ratio is characterized theoretically and experimentally in the underwater base excitation problem. In the second part of this work, Ultrasonic Acoustic Energy Transfer via piezoelectric transduction is investigated theoretically and experimentally. Contactless energy transfer using acoustic excitation offers larger distances of power transmission as compared to well-studied inductive method. Various transmitter configurations (e.g. spherical, cylindrical, and focused) are explored for energy transfer to a piezoelectric receiver bar (operating in the longitudinal/thickness mode) that is shunted to a generalized resistive-reactive circuit. Fixed-free and free-free mechanical boundary conditions of the receiver are explored in detail. The resulting multiphysics analytical model framework is compared with finite-element simulations and experiments conducted in fluid (water and oil). Optimal piezoelectric receiver material and electrical loading conditions are sought for performance and bandwidth enhancement.

Energy harvesters collect and convert energy available in the environment into useful electrical power to satisfy the power requirements of autonomous systems. Vibration energy is a prevalent source of waste energy in industrial and built environments. Vibration-based energy harvesters, or vibration-based micro power generators (VBMPGs), utilize a transducer, a mechanical oscillator in this application, to capture kinetic energy from environmental vibrations and to convert it into electrical energy using electromagnetic, electrostatic, or piezoelectric transduction mechanisms. A key design feature of all VBMPGs, regardless of their transduction mechanism, is that they are optimally tuned to harvest vibration energy within a narrow frequency band in the neighborhood of the natural frequency of the oscillator. Outside this band, the output power is too low to be conditioned and utilized. This limitation is exacerbated by the fact that VBMPGs are also designed to have high quality factors to minimize energy dissipation, further narrowing the optimal operating frequency band. Vibrations in most environments, however, are random and wideband. As a result, VBMPGs can harvest energy only for a relatively limited period of time, which imposes excessive constraints on their usability. A new architecture for wideband VBMPGs is the main contribution of this thesis. The new design is general in the sense that it can be applied to any of the three transduction mechanisms listed above. The linear oscillator is replaced with a piecewise-linear oscillator as the energy-harvesting element of the VBMPG. The new architecture has been found to increase the bandwidth of the VBMPG during a frequency up-sweep, while maintaining the same bandwidth in a frequency downsweep. Experimental results show that using the new architecture results in a 313% increase in the width of the bandwidth compared to that produced by traditional architecture. Simulations show that under random-frequency excitations, the new architecture collects more energy than traditional architecture. In addition, the knowledge acquired has been used to build a wideband electromagnetic VBMPG using MicroElectroMechanical Systems, MEMS, technology. This research indicates that a variety of piecewise-linear oscillators, including impact oscillators, can be implemented on MPG structures that have been built using MEMS technology. When the scale of the MPGs is reduced, lower losses are likely during contact between the moving oscillators and the stopper, which will lead to an increase in bandwidth and hence in the amount of energy collected. Finally, a design procedure has been developed for optimizing such wideband MPGs. This research showed that wideband MPGs require two design optimization steps in addition to the traditional technique, which is used in all types of generators, of minimizing mechanical energy losses through structural design and material selection. The first step for both regular and wideband MPGs minimizes the MPG damping ratio by increasing the mass and stiffness of the MPG by a common factor until the effect of size causes the rate at which energy losses increase to accelerate beyond that common factor. The second step, which is specific to wideband MPGs, tailors the output power and bandwidth to fit the Probability Density Function, PDF, of environmental vibrations. A figure of merit FoM was devised to quantify the quality of this fit. Experimental results show that with this procedure, the bandwidth at half-power level increases to more than 600% of the original VBMPG bandwidth.

Energy harvesters collect and convert energy available in the environment into useful electrical power to satisfy the power requirements of autonomous systems. Vibration energy is a prevalent source of waste energy in industrial and built environments. Vibration-based energy harvesters, or vibration-based micro power generators (VBMPGs), utilize a transducer, a mechanical oscillator in this application, to capture kinetic energy from environmental vibrations and to convert it into electrical energy using electromagnetic, electrostatic, or piezoelectric transduction mechanisms. A key design feature of all VBMPGs, regardless of their transduction mechanism, is that they are optimally tuned to harvest vibration energy within a narrow frequency band in the neighborhood of the natural frequency of the oscillator. Outside this band, the output power is too low to be conditioned and utilized. This limitation is exacerbated by the fact that VBMPGs are also designed to have high quality factors to minimize energy dissipation, further narrowing the optimal operating frequency band. Vibrations in most environments, however, are random and wideband. As a result, VBMPGs can harvest energy only for a relatively limited period of time, which imposes excessive constraints on their usability. A new architecture for wideband VBMPGs is the main contribution of this thesis. The new design is general in the sense that it can be applied to any of the three transduction mechanisms listed above. The linear oscillator is replaced with a piecewise-linear oscillator as the energy-harvesting element of the VBMPG. The new architecture has been found to increase the bandwidth of the VBMPG during a frequency up-sweep, while maintaining the same bandwidth in a frequency downsweep. Experimental results show that using the new architecture results in a 313% increase in the width of the bandwidth compared to that produced by traditional architecture. Simulations show that under random-frequency excitations, the new architecture collects more energy than traditional architecture. In addition, the knowledge acquired has been used to build a wideband electromagnetic VBMPG using MicroElectroMechanical Systems, MEMS, technology. This research indicates that a variety of piecewise-linear oscillators, including impact oscillators, can be implemented on MPG structures that have been built using MEMS technology. When the scale of the MPGs is reduced, lower losses are likely during contact between the moving oscillators and the stopper, which will lead to an increase in bandwidth and hence in the amount of energy collected. Finally, a design procedure has been developed for optimizing such wideband MPGs. This research showed that wideband MPGs require two design optimization steps in addition to the traditional technique, which is used in all types of generators, of minimizing mechanical energy losses through structural design and material selection. The first step for both regular and wideband MPGs minimizes the MPG damping ratio by increasing the mass and stiffness of the MPG by a common factor until the effect of size causes the rate at which energy losses increase to accelerate beyond that common factor. The second step, which is specific to wideband MPGs, tailors the output power and bandwidth to fit the Probability Density Function, PDF, of environmental vibrations. A figure of merit FoM was devised to quantify the quality of this fit. Experimental results show that with this procedure, the bandwidth at half-power level increases to more than 600% of the original VBMPG bandwidth.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 192-196).

The piezoelectric transducer for vibration-energy harvesting is constructed of a piezoelectric layer, bottom electrode and a top electrode. In order to obtain an appropriate transducer for the low-frequency operating; environmentally-friendly and long-term, the flexible substrate, the piezoelectric layer, and the additional mass-loading (tip mass) have been investigated thoroughly. This study investigates the feasibility of a high-performance ZnO and AlN based piezoelectric transducer for vibration-energy harvesting applications. Firstly, the piezoelectric transducer is constructed of a Cu/ZnO/ITO/PET structure. Both scanning electron microscopy and X-ray diffraction indicate that, among the favorable characteristic of the ZnO piezoelectric film include a rigid surface structure and a high c-axis preferred orientation. Hence, an open circuit voltage of 1.87 V for the ZnO piezoelectric transducer at a vibration frequency of 100 Hz is obtained by an oscilloscope. After rectifying and filtering, the output power of the generator exhibits an available benefit of 0.07 £gW/cm2 with the load resistance of 5 M£[. Secondly, this investigation introduces novel means of integrating high-performance piezoelectric transducers using single-sided ZnO and AlN films with a flexible stainless steel substrate (SUS304). Hence, the SUS304 substrate exhibits the long-term stability under vibration. The single-sided ZnO and AlN transducers are deposited on the SUS304 substrate at a temperature of 300 oC by an RF magnetron sputtering system. Scanning electron microscopy and X-ray diffraction of piezoelectric films reveal a rigid surface structure and a high c-axis-preferred orientation. A mass loading at the front-end of the cantilever is critical to increase the amplitude of vibration and the power generated by the piezoelectric transducer. The open circuit voltage of the single-sided ZnO power generator is 10.5 V. After rectification and filtering through a capacitor with a capacitance of 33 nF, the output power of the single-sided ZnO generators exhibited a specific power output of 1.0 £gW/cm2 with a load resistance of 5 M£[. Finally, this investigation fabricates double-sided piezoelectric transducers for harvesting vibration-power. The double-sided piezoelectric transducer is constructed by depositing piezoelectric thin films on both the front and the back sides of SUS304 substrate. The titanium (Ti) and platinum (Pt) layers were deposited using a dual-gun DC sputtering system between the piezoelectric thin film and the back side of the SUS304 substrate. Scanning electron microscopy and X-ray diffraction of piezoelectric films reveal a rigid surface structure and highly c-axis-preferring orientation. The maximum open circuit voltage of the double-sided ZnO power transducer is approximately 18 V. After rectification and filtering through a 33 nF capacitor, a specific power output of 1.3 £gW/cm2 is obtained from the double-sided ZnO transducer with a load resistance of 6 M£[. The variation of the power output of ¡Ó0.001% is obtained after 24-hour continuous test. The maximum open circuit voltage of the double-sided AlN power transducer is approximately 20 V. After rectification and filtering through a 33 nF capacitor, a specific power output of 1.462 £gW/cm2 is obtained from the double-sided AlN transducer with a load resistance of 7 M£[.

This thesis has been motivated by the idea of harvesting the energy from ambient vibrations via nonlinear dynamics of the parametric pendulum. It aims to cover those aspects of the pendulum dynamics, which are relevant for energy extraction purposes and have not been addressed in previous studies. A simple system like parametric pendulum can experience variety of responses. One of them is rotary motion, which is characterised by significantly higher kinetic energy than oscillations and thus has a potential of delivering more energy, when subjected to the parametric excitation. Initially, a preliminary study on the dynamics of parametric pendulum has been conducted. This involved comparison of oscillatory and rotary responses with a view to application in energy harvesting, numerical continuation of rotary solutions and developing a control method for initiating and maintaining the desired response. As a next step, different forcing configurations have been considered, including pendulum excited along a tilted axis and a combined excitation, where pendulum additionally performs rocking action. The influence of the forcing arrangement on the lower limit of stability of rotary motion has been examined. The vibrations which can be observed in the environment are rarely perfectly harmonic. To provide more realistic results, the response of the pendulum under noisy excitation has been studied. Different types of noise have been considered and their influence on the pendulum rotation examined. One of the major energy sources, which could be utilised are the oscillating ocean surfaces. Therefore, a stochastic model of the sea wave has been constructed and the response of the pendulum system studied under parametric excitation by a wave profile. Finally, taking into account the imbalanced forces which rotating pendulum exerts on the supporting base, the model has been extended to a system of two pendulums. Synchronization in such a system was studied. The influence of the synchronization mode on the rotation of the pendulums and on the stability of supporting structure was considered. All of the numerical results presented in this thesis have been verified experimentally to ensure good correspondence.

Vibration energy harvesting has been widely investigated by academia and industry in the past decade with focus on developing distributed power sources. One of the prime goals of energy harvesters is to provide power to wireless sensors allowing for the placement of these sensors in the remote and inaccessible areas where battery is not an option. Electromechanical modeling approaches have been developed for enhancing the mechanical to electrical conversion efficiencies utilizing electromagnetic, piezoelectric, and magnetostrictive mechanisms. Models based upon the constitutive equations for these three conversion mechanisms, supported by extensive experimental results available in literature, suggest that power requirement through energy harvesters can be met only when the total volume is in the range of 1-100 cm3. There exists a critical volume of 0.5 cm³ at which above which the electromagnetic mechanism exhibits higher power density as compared to the other mechanisms. Therefore, in this thesis electromagnetic energy conversion was adopted to develop high power energy harvesters. We also present a novel vibration energy harvesting method which rivals the power density and bandwidth of the traditional methods. The overarching theme throughout the design process was selecting the structure and fabrication methodology that facilitates the transition of the technology. The experimental models were characterized at accelerations and frequencies typically found in the environmental vibration sources. The thesis provides in-depth the design, modeling, and characterization of a vibration energy harvester which creates relative motion differently than the conventional harvesters. Conventional designs rely on amplifying the original source displacement operating at the resonance condition. In the harvester design proposed in this thesis, the relative motion is created by cancelling the vibration at one location and transferring the source vibration directly to another location by combining a vibration isolator with a vibration absorber. In this novel configuration, termed as Direct Vibration Harvester (DVH), the energy is harvested directly from the vibrating source mass rather than a vibrating seismic mass attached to the source increasing the harvesting bandwidth and power density. Four bar magnet and magnetic levitation architectures were modified and modeled to reach closer to the theoretical maximum power densities. Extensive FEM was utilized to understand the performance limitations of the existing structures and the results from this analysis paved the pathway towards the development of the DVH. �A comparative analysis of the performance of the DVH with the traditional harvesting methods in terms of normalized power output and bandwidth was conducted. Performance improvements of DVH required development of the high efficiency rotational generators as linear to rotational conversion occurs in the DVH. The optimized rotational generator was modeled and all the predicted performance metrics were validated through experiments. The generator was applied towards the fabrication of DVH and also in a micro windmill. The power density of the micro windmill was found to be better than all the other results reported in literature. Extensive fluid and structural modeling was conducted to tailor the performance of the micro windmill in the desired wind speed range. Combined, this thesis provides significant advancement on many fronts. It pushes the magnetic levitation and four-bar mechanism harvester systems to their theoretical limits. It demonstrates a novel direct vibration harvester that has the possibility of surpassing the power density and bandwidth of all the known vibration harvester with large magnitude of output power. It provides a design process for an efficient small scale electromagnetic generator that can form for the backbone of many rotational and linear harvesters. This generator was used to develop the world's highest power density micro windmill in the small wind speed range. / Ph. D.

No description available.

Vibration-based energy harvesting has been investigated by several researchers over the last decade. The ultimate goal in this research field is to power small electronic components (such as wireless sensors) by using the vibration energy available in their environment. Among the basic transduction mechanisms that can be used for vibration-to-electricity conversion, piezoelectric transduction has received the most attention in the literature. Piezoelectric materials are preferred in energy harvesting due to their large power densities and ease of application. Typically, piezoelectric energy harvesters are cantilevered structures with piezoceramic layers that generate alternating voltage output due to base excitation. This work presents distributed-parameter electromechanical models that can accurately predict the coupled dynamics of piezoelectric energy harvesters. First the issues in the existing models are addressed and the lumped-parameter electromechanical formulation is corrected by introducing a dimensionless correction factor derived from the electromechanically uncoupled distributed-parameter solution. Then the electromechanically coupled closed-form analytical solution is obtained based on the thin-beam theory since piezoelectric energy harvesters are typically thin structures. The multi-mode electromechanical frequency response expressions obtained from the analytical solution are reduced to single-mode expressions for modal vibrations. The analytical solutions for the electromechanically coupled voltage response and vibration response are validated experimentally for various cases. The single-mode analytical equations are then used for deriving closed-form relations for parameter identification and optimization. Asymptotic analyses of the electromechanical frequency response functions are given along with expressions for the short-circuit and the open-circuit resonance frequencies. A simple experimental technique is presented to identify the optimum load resistance using only a single resistor and an open-circuit voltage measurement. A case study is given to compare the power generation performances of commonly used monolithic piezoceramics and novel single crystals with a focus on the effects of plane-stress material constants and mechanical damping. The effects of strain nodes and electrode configuration on piezoelectric energy harvesting are discussed theoretically and demonstrated experimentally. An approximate electromechanical solution using the assumed-modes method is presented and it can be used for modeling of asymmetric and moderately thick energy harvester configurations. Finally, a piezo-magneto-elastic energy harvester is introduced as a non-conventional broadband energy harvester. / Ph. D.