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Energy harvesting technology has the ability to create autonomous, self-powered electronic systems that do not rely on battery power for their operation. The term energy harvesting describes the process of converting ambient energy surrounding a system into useful electrical energy through the use of a specific material or transducer. A widely studied form of energy harvesting involves the conversion of mechanical vibration energy into electrical energy using piezoelectric materials, which exhibit electromechanical coupling between the electrical and mechanical domains. Typical piezoelectric energy harvesting systems are designed as add-on systems to a host structure located in a vibration rich environment. The added mass and volume of conventional vibration energy harvesting designs can hinder to the operation of the host system. The work presented in this dissertation focuses on advancing piezoelectric energy harvesting concepts through the introduction of multifunctionality in order to alleviate some of the challenges associated with conventional piezoelectric harvesting designs. The concept of multifunctional piezoelectric self-charging structures is explored throughout this work. The operational principle behind the concept is first described in which piezoelectric layers are directly bonded to thin-film battery layers resulting in a single device capable of simultaneously harvesting and storing electrical energy when excited mechanically. Additionally, it is proposed that self-charging structures be embedded into host structures such that they support structural load during operation. An electromechanical assumed modes model used to predict the coupled electrical and mechanical response of a cantilever self-charging structure subjected to harmonic base excitation is described. Experimental evaluation of a prototype self-charging structure is then performed in order to validate the electromechanical model and to confirm the ability of the device to operate in a self-charging manner. Detailed strength testing is also performed on the prototype device in order to assess its strength properties. Static three-point bend testing as well as dynamic harmonic base excitation testing is performed such that the static bending strength and dynamic strength under vibration excitation is assessed. Three-point bend testing is also performed on a variety of common piezoelectric materials and results of the testing provide a basis for the design of self-charging structures for various applications. Multifunctional vibration energy harvesting in unmanned aerial vehicles (UAVs) is also investigated as a case study in this dissertation. A flight endurance model recently developed in the literature is applied to model the effects of adding piezoelectric energy harvesting to an electric UAV. A remote control foam glider aircraft is chosen as the test platform for this work and the formulation is used to predict the effects of integrating self-charging structures into the wing spar of the aircraft. An electromechanical model based on the assumed modes method is then developed to predict the electrical and mechanical behavior of a UAV wing spar with embedded piezoelectric and thin-film battery layers. Experimental testing is performed on a representative aluminum wing spar with embedded self-charging structures in order to validate the electromechanical model. Finally, fabrication of a realistic fiberglass wing spar with integrated piezoelectric and thin-film battery layers is described. Experimental testing is performed in the laboratory to evaluate the energy harvesting ability of the spar and to confirm its self-charging operation. Flight testing is also performed where the fiberglass spar is used in the remote control aircraft test platform and the energy harvesting performance of the device is measured during flight. / Ph. D.

The focus of this research was to create a linear motor that could easily be packaged and still perform the same task of the current DC motor linear device. An incremental linear motor design was decided upon, for its flexibility in which the motor can be designed. To replace the current motor it was necessary to develop a high force, high speed incremental linear motor. To accomplish this task, piezoelectric actuators were utilized to drive the motor due their fast response times and high force capabilities. The desired overall objectives of the research is to create an incremental linear motor with the capability of moving loads up to one hundred pounds and produce a velocity well over one inch per second. To aid the design process a lumped parameter model was created to simulate the motor's performance for any design parameter. Discrepancies occurred between the model and the actual motor performance for loads above 9.1 kilograms (20 pounds). The resulting model, however, was able to produce a good approximation of the motor's performance for the unloaded and lightly loaded cases. The phase one design was limited by time constraints so a relatively low risk design was produced. The resulting incremental linear motor produced a velocity of 4.9 mm/sec (0.2 in/sec) at a drive frequency of 50 Hz. The velocity of the motor was limited by the drive frequency that the amplifiers could produce. The motor was found to produce a respectable stall load of 17 kilograms (38 pounds). The stall load of the phase one design was severely limited by clearance losses. An analysis of the motor's performance was conducted, possible improvements and future work recommendations for a phase two design are presented. / Master of Science

Currently in the marketplace, one of the important goals is to improve quality, and reliability. There is great interest in the engineering community to develop a field calibration technique concerning piezoelectric pressure sensor to reduce cost and improve reliability. This paper summarizes the algorithm used to characterize and develop a model for a piezoelectric pressure transducer. The basic concept of the method is to excite the sensor using an electric force to capture the signature characteristic of the pressure transducer. This document presents the frequency curve fitted model based on the high frequency excitation of the piezoelectric pressure transducer. It also presents the time domain model of the sensor. The time domain response of the frequency curve fitted model obtained in parallel with the frequency response of the time domain model and the comparison results are discussed. Moreover, the relation between model parameters and sensitivity extensively is investigated. In order to detect damage and monitor the condition of the sensor on line the resonance frequency comparison method is presented. The relationship between sensitivity and the resonance frequency characteristic of the sensor extensively is investigated. The method of resonance monitoring greatly reduces the cost of hardware. This work concludes with a software implementation of the signature comparison of the sensor based on a study of the experimental data. The software would be implemented in the control system. / Master of Science

Given the ever-growing need for device autonomy and renewable sources of energy, energy harvesting has become an increasingly popular field of research. This research focuses on energy harvesting using the piezoelectric effect, from vibrating membrane structures by converting mechanical energy into electric energy. Specific applications of this research include powering components of bio-inspired micro air vehicles (MAVs), which require long range with as little regular maintenance as possible, and powering sensors for structural health monitoring on otherwise inaccessible locations (the roof of the Denver Int'l Airport is a good example). Coming up with an efficient, high-fidelity model of these systems allows for design optimization without the extensive use of experimental testing, as well as a deeper understanding of the physics involved. These are the twin goals of this research. This work describes a modeling algorithm using COMSOL, a multi-physics software, to predict the structural mechanics of and subsequent power harvested from a piezoelectric patch placed on a prestressed membrane structure. The model is verified by an FE comparison of the modeled system's dynamic response. For a 0.5 x 0.5 x 0.001 m nylon membrane with a 0.1 x 0.1 x 0.001 m piezoelectric patch placed on its corner, a maximum power output of ~10 microwatts was achieved, using a resistance of 100 Ohms and exciting the system around resonance. When the patch was placed on the side of the membrane, the power output was ~100 milliwatts. The ultimate goal is to estimate the energy harvested by a network of these piezoelectric patches and optimize the harvesting system based on the size, shape and location of the patches. / Master of Science

The prime objective of this dissertation is to design, synthesize and characterize lead-free piezoelectric based magnetostrictive components based magnetoelectric (ME) composites that exhibit self-bias characteristics and high amplitude of ME coupling. The secondary goal of this thesis was to lay down the foundation for nanoscale and flexible magnetoelectric devices. Self-biased ME effect was investigated in lead-free three-phase laminate composites. This effect is characterized by non-zero remanent ME responses at zero magnetic bias field (Hbias). It was revealed that the self-biased ME effects can be observed in three-phase laminate composites consisting of piezoelectric material and two dissimilar magnetostrictive materials. On applying Hbias to the laminates in bending mode configuration, the ME responses were found to exhibit hysteretic behaviors with remanent ME responses. The shape of hysteretic ME response could be controlled by adjusting the magnetic interactions and piezoelectric properties. Further, converse magnetoelectric (CME) responses in bending-mode three-phase laminates exhibited hysteretic behaviors with similar magnitudes during Hbias sweep as it was generated directly by applying ac voltage (Vac) without any external Hbias. Lead-free (1 - x) [0.948 K0.5Na0.5NbO3 - 0.052 LiSbO3] - x Ni0.8Zn0.2Fe2O4 (KNNLS-NZF) compositions were synthesized for optimizing ME properties of particulate composites. Island-matrix microstructure was developed to improve the magnitude of ME coupling effect by overcoming the problems found in conventional particulate composites. The structure lead to improvement of ME coefficient with maximum magnitude of 20.14 mV/cm ae as well as decrease of optimum Hbias of < 500 Oe in the composition of 0.7 KNNLS - 0.3 NZF particulate composites. Room-temperature ME phase diagram of (1 - x) BaTiO3 - x BiFeO3 materials (BT - x BFO, x = 0.025 - 1.0) was investigated for designing compositions suitable for thin film devices. The BT - x BFO compositions in narrow range of x = 0.71 - 0.8 were found to exhibit good piezoelectric, dielectric and magnetic properties simultaneously. The room temperature ME coefficient was found to be maximum with high magnitude of 0.87 mV/cmOe in the optimized composition of x = 0.725.This composition was found to consist of local monoclinic distortions with average rhombohedral symmetry as confirmed by detailed structural analysis through Raman spectroscopy and atomic pair distribution functions (PDFs). MnFe2O4 (MFO)-Ni core-shell nanoparticles were synthesized and characterized for developing tunable devices such as memristor. The MFO nanoparticles synthesized by solvothermal method exhibited diameter of 200 nm, mean primary particle size of 15 nm, high saturation magnetization of 74 emu/g and coercivity of 89 Oe. Ni encapsulation on MFO nanoparticles was performed by aqueous ionic coating method. Ni shells with uniform thickness of 1 nm were coated on MFO nanoparticles by this method. In order to develop future nanoscale dual phase energy harvesters and magnetic field sensors, vertically-aligned piezoelectric nanorods were synthesized. In the initial attempt, Pb(Zr0.52Ti0.48)O3 (PZT) was used to verify the feasibility of developing one dimensional (1D) piezoelectric nanostructures with controlled diameter and height. For the 1D nanostructure, well-ordered anodic aluminum oxide (AAO) templates were prepared by two step aluminum anodizing. The PZT nanorods were synthesized by vacuum infiltration of PZT precursor solutions and exhibited uniform diameter of 90 nm and aspect ratio of 10 with vertical in respect to the Pt-Si substrate. The piezo-response of PZT nanorods showed good magnitude owing to the reduced clamping effect from the substrate. Attempt towards the development of flexible tunable devices that possess magnetic field sensing and actuation ability was made in the later part of the thesis. The electroactive polymeric actuators in the form of Polypyrrole (PPy) / Au / Polyvinylidene fluoride (PVDF) / Au / Polypyrrole (PPy) were synthesized and the process flow was optimized. Pore size and thickness of PVDF layer was adjusted by changing the solvent, viscosity and drying temperature. Different types of electrolyte solutions were investigated to improve the strain and response time. The actuators exhibited high deflection of 90 % with fast response of 50% deflection per second. Dual-functional structure in the form of  PPy-MFO / Au / PVDF / Au / PPy-MFO was developed by PPy polymerization including MFO nanoparticles via cyclovoltammetric method. / Ph. D.

A piezoceramic actuator used for structural control behaves electrically as a nearly pure capacitance. When conventional amplifiers are used to drive these actuators, the current and voltage is close to 90 degrees out of phase. This causes the power factor (PF) of the load to be close to zero and results in excessive power requirements. This thesis reports the results of a study of the following question: What effect does applying power factor correction methods to piezoceramic actuators have on their power consumption characteristics? A subproblem we explored was to detennine the qualitative relationship between the power consumption of a piezoceramic actuator and the damping that actuator added to a structure. To address the subproblem, a feedback control experiment was built which used a ceramic piezoceramic actuator and a strain rate sensor configured to add damping to a cantilevered beam. A disturbance was provided by a shaker attached to the beam. The power consumption of the actuator was determined by measuring the current and voltage of the signal to the actuator. The energy dissipated in the beam by the feedback control loop was assumed to be modeled by an ideal structural damping model. A model relating structural damping as a function of the apparent power consumed by the actuator was developed, qualitatively verified, and physically justified. Power factor correction methods were employed by adding an inductor in both parallel to and in series with the piezoceramic actuator. The inductance values were chosen such that each inductor-capacitor (LC) circuit was in resonance at the second natural frequency of the beam. Implementing the parallel LC circuit reduced the current consumption of the piezoceramic actuator by 75% when compared to the current consumption of the actuator used without an inductor. Implementing the series LC circuit produced a 300% increase in the voltage applied to the actuator compared to the case when no inductor was used. In both cases, employing power factor correction methods corrected the power factor to near unity and reduced the apparent power by 12 dB. A theoretical model of each circuit was developed. The analytical and empirical results are virtually identical. The results of this study can be used to synthesize circuits to modify piezoceramic actuators, reducing the voltage or current requirements of the amplifiers used to drive those actuators / Master of Science

The magnetoelectric (ME) effect, i.e., the induction of magnetization by an applied electric field (E) or a polarization by an applied magnetic field (H), is of great interest to researchers due to its potential applications in magnetic sensors. Moreover, the ME effect in laminate composites is known to be much higher than in single phase and particulate composites due to combination of the magnetostrictive and piezoelectric effects in the individual layers. Given that the highest ME coefficient have been found in Metglas/piezo-fiber laminate composites, this study was designed to investigate and enhance the magnetoelectric (ME) effect in Metglas/piezo-fiber laminate composites, as well as develop their potential for magnetic sensor applications. To initiate this investigation, a theoretical model was derived to analyze the thickness effect of the magnetostrictive, piezoelectric, epoxy and Kapton layers on the ME coefficient. As a result, the importance of the coupling effect by epoxy layers was revealed. I used spin-coating, vacuum bagging, hot pressing, and screen printing techniques to decrease the thickness of the epoxy layer in order to maintain homogeneity, and to obtain good repeatability of the 16 ME laminates fabricated at one time. This protocol resulted in a more efficient way to induce self-stress to Metglas/PZT laminates, which is essential for increasing the ME coefficient. With an enhanced ME effect in the Metglas/piezo-fiber laminates, magnetic field sensitivity could then be increased. An ME sensor unit, which consisted of a Metglas/PMN-PT laminate and a low noise charge amplifier, had a magnetic field sensitivity of 10 pT/Hz0.5 in a well-shielded environment. Stacking four of these ME laminates could further increase the signal-to-noise (SNR) ratio. I studied the optimized distance between a pair of Metglas/PZT ME laminates. A stack of up to four ME sensors was constructed to decrease the equivalent magnetic noise. The magnetic field sensitivity was effectively enhanced compared to a single laminate. Finally, a number of four Metglas/PZT sensor units array was constructed to further increase the sensitivity. ME laminate composites operated in passive mode have typically required an external magnetic bias field in order to maximize the value of the piezomagnetic coefficient, which has many drawbacks. I studied the ME effect in an Ni/Metglas/PZT laminate at zero bias field by utilizing the remnant magnetization between the Ni and Metglas layers. To further enhance this effect, annealed Metglas was bonded on the Metglas/PZT laminate since it is known that hard-soft ferromagnetic bilayers generate built-in magnetic field in these Metglas layers. As a result, giant αME values could be achieved at a zero bias field at low frequency range or at electromechanical resonance (EMR). The sensor unit consisting of self-biased ME laminate arrays is considerably smaller compared to a unit that uses magnet-biased ME laminates. Introducing the converse ME effect and nonlinear ME effect in Metglas/piezo-fiber laminates affords a variety of potential applications. Therefore, I theoretically and experimentally studied converse ME effects in laminates with longitudinally magnetized and longitudinally poled, or (L-L) mode. The optimum structure for producing the maximum effect was obtained for Metglas/PZT laminates. Additionally, the optimum structure and materials for enhancing the nonlinear ME effect in Metglas/PZT laminates are reviewed herein. In particular, this study revealed that modulating the EMR in laminates with high-Q piezo-fibers could enhance the SNR. The stress effect on nonlinear ME effect is also discussed—namely that magnetic field sensitivities can be enhanced by this modulation-demodulation technique. / Ph. D.

Energy efficient appliances and devices are becoming increasingly necessary as emissions from electricity production continue to increase the severity of global warming. Many of such appliances have not been substantially redesigned since their creation in the early 1900s. One device in particular which has arguably changed the least and consumes the most energy during use is the electric clothes dryer. The common form of this technology in the United States relies on the generation of thermal energy by passing electrical current through a metal. The resulting heat causes liquid within the clothing to evaporate where humid air is ejected from the control volume. While the conversion of energy from electrical to thermal through a heating element is efficient, the drying characteristics of fabrics in a warm humid environment are not, and much of the heat inside of the dryer does not perform work efficiently. In 2016, researchers at Oak Ridge National Laboratory in Knoxville, Tennessee, proposed an alternative mechanic for the drying of clothes which circumvents the need for thermal energy. This method is called direct-contact ultrasonic clothes drying, utilizing atomization through direct mechanical coupling between mesh piezoelectric transducers and wet fabric. During the atomization process, vertical oscillations of a contained liquid, called Faraday excitations, result in the formation of standing waves on the liquid surface. At increasing amplitudes and frequencies of oscillation, wave peaks become extended and form "necks" connecting small secondary droplets to the bulk liquid. When the oscillation reaches an acceleration threshold, the droplet momentum is sufficient to break the surface tension of the neck and enable the droplets to travel away from the liquid. For smaller drops where surface tension is high, a larger magnitude of acceleration is needed to reach the critical neck lengths necessary for droplet ejection. The various pore sizes within the many fabrics comprising our clothing results in many sizes of droplets retained by the fabric, affecting the rate of atomization due to the differences in surface tension. In this study, we will investigate the physical processes related to the direct contact ultrasonic drying process. Beginning with the electrical actuation of the transducer used in the world's first prototype dryer, we will develop an electromechanical model for predicting the resulting deformation. Various considerations for the material properties and geometry of the transducer will be made for optimizing the output acceleration of the device. Next, the drying rates of fabrics in contact with the transducer will be modeled for identification of parameters which will facilitate timely and energy efficient drying. This task will identify the first ever mechanically coupled drying equation for fabrics in contact with ultrasonic vibrations. The ejection rate of the water atomized by the transducer and passed through microchannels to facilitate drying will then be physically investigated to determine characteristics which may improve mass transport. Finally, future considerations and recommendations for the development of ultrasonic drying will be made as a result of the insight gained by this investigation. / Doctor of Philosophy / Energy efficient appliances and devices are becoming increasingly necessary as emissions from electricity production continue to increase the severity of global warming. Many of such appliances have not been substantially redesigned since their creation in the early 1900s. One device in particular which has arguably changed the least and consumes the most energy during use is the electric clothes dryer. The common form of this technology in the United States relies on the generation of thermal energy by passing electrical current through a metal. The resulting heat causes liquid within the clothing to evaporate where the humid air is ejected from the control volume. While the conversion of energy from electrical to thermal through a heating element is efficient, the drying characteristics of fabrics in a warm humid environment are not, and much of the heat inside of the volume does not perform drying as efficiently as possible. In 2016, researchers at Oak Ridge National Laboratory in Knoxville, Tennessee, proposed an alternative mechanism for the drying of clothes which circumvents the need for thermal energy. This method is called direct-contact ultrasonic clothes drying, and utilizes a vibrating disk made of piezoelectric and metal materials to physically turn the water retained in clothing into a mist, which can be vented away leaving behind dry fabric. This method results in the water leaving the fabric at room temperature, rather than being heated, which bypasses the need for a substantial amount of energy to convert from the liquid to gas phase. The first ever prototype dryer shows the potential of being twice as efficient as conventional dryers. This investigation is based around improving the device atomizing the water within the clothing, as well as understanding physical processes behind the ultrasonic drying process. These tasks will be conducted through experimental measurements and mathematical models to predict the behavior of the atomizing device, as well as computer software for both the parameters experimentally measured, and items which cannot be measured such as the flow in very small channels. The conclusions of this study will be recommendations for the future development of direct contact ultrasonic drying technology.

Power harvesting, energy harvesting, power scavenging, and energy scavenging are four terms commonly used to describe the process of extracting useful electrical energy from other ambient energy sources using special materials called transducers that have the ability to convert one form of energy into another. While the words power and energy have vastly different definitions, the terms "power harvesting" and "energy harvesting" are used interchangeably throughout much of the literature to describe the same process of extracting electrical energy from ambient sources. Even though most of the energy coupling materials currently available have been around for decades, their use for the specific purpose of power harvesting has not been thoroughly examined until recently, when the power requirements of many electronic devices has reduced drastically. The overall objective of this research is to typify the power source characteristics of various transducer devices in order to find some basic way to compare the relative energy densities of each type of device and, where possible, the comparative energy densities within subcategories of harvesting techniques. Included in this research is also a comparison of power storage techniques, which is often neglected in other literature sources. An initial analysis of power storage devices explores the background of secondary (rechargeable) batteries and supercapacitors, the advantages and disadvantages of each, as well as the promising characteristics of recent supercapacitor technology developments. Also explored is research into the effectiveness of piezoelectric energy harvesting for the purpose of battery charging, with particular focus on the current output of piezoelectric harvesters. The first objective involved presenting and verifying a model for a cantilever piezoelectric bimorph. Next, an investigation into new active fiber composite materials and macro fiber composite devices utilizing the d31 coefficient is performed in comparison to a monolithic piezoelectric bimorph. The information gathered here was used to design a two bimorph device termed the mobile energy harvester (MEH). Worn by a human being at the waste level, the MEH harvests energy from each footfall during walking or running. The next objective involved characterizing small temperature gradient (less than 200 oC) thermoelectric generators (TEGs). Four TEGs were linked in series and joined with a specially made aluminum base and fin heat sink. This device was then mounted to the exhaust system of an automobile and proved capable of recharging both an 80 and a 300 milliamp-hour battery. A switching circuit concept to step up the output voltage is also presented. However, the circuit proves somewhat difficult to implement, so an alternative DC/DC device is proposed as a possible solution. With the advent of highly efficient, low voltage DC to DC converters, it is shown that their high current, low voltage output can be converted to a higher voltage source that is suitable for many electronic and recharging applications. As extensive literature exists on the capabilities of photovoltaic and electromagnetic energy harvesting, no original experimentation is presented. Instead, only a brief overview of the pertinent technological advances is provided in this document for the purpose of comparison to piezoelectric and thermoelectric energy harvesting. The main research focus, as described above, is dedicated to designing and performing original experiments to characterize cutting edge piezoelectric and thermoelectric transducer materials. To conclude and unify the document, the final section compares the power harvesting techniques with one another and introduces methods of combining them to produce a hybrid, multiple energy domain harvesting device. A piezoelectric-electromagnetic harvesting combination device is presented and scrutinized, revealing that such a device could improve the amount of energy extracted from a single harvesting unit. The research presented here not only expands on the present understanding of these materials, but also proposes a new method of creating a hybrid power harvesting device utilizing two of the energy coupling domains, electromechanical and piezoelectric. The goal is to maximize the harvested energy by tapping into as many ambient sources as are available and practical. / Master of Science