Browsing by Subject "piezoelectric"
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Item A Single Inductor, Multiple Input Piezoelectric Interface Circuit Capable of Harvesting Energy from Asynchronously Vibrating Sources(2014-10-23) Ribeiro, RolandThe energy harvesting industry has seen steady growth in recent years. This growth has been driven by the increasing demand for remote sensing, implantable technologies, and increased battery life in mobile and hand held devices. Due to the limited amount of energy available from ambient sources, any system that attempts to harness energy from them should necessarily be highly efficient to make the net output power useful. A lot of work has been done on minimizing losses in piezoelectric energy harvesters. Most of this has however been limited to harvesters with single vibration sources or multiple sources vibrating synchronously. This work presents a multiple input piezoelectric energy harvester capable of harvesting from multiple piezoelectric energy sources vibrating asynchronously (at different frequencies, or at the same frequency but in different phases) using a single inductor. The use of a single inductor eliminates the extra quiescent power consumption, component count, printed circuit board real estate that would have been incurred by using a one inductor per input device. The inductor is time shared between three input devices using a digital control circuit which regulate access to the inductor while avoiding any destructive interaction between the input devices. The chip was designed in a 0.18?m technology and achieves a conversion efficiency of 60%. Testing with three asynchronously vibrating sources shows that the chip extracts maximum power from all inputs simultaneously, independent of vibration frequency or phase.Item Effective properties of three-phase electro-magneto-elastic multifunctional composite materials(Texas A&M University, 2005-02-17) Lee, Jae SangCoupling between the electric field, magnetic field, and strain of composite materials is achieved when electro-elastic (piezoelectric) and magneto-elastic (piezomagnetic) particles are joined by an elastic matrix. Although the matrix is neither piezoelectric nor piezomagnetic, the strain field in the matrix couples the E field of the piezoelectric phase to the B field of the piezomagnetic phase. This three-phase electro-magneto-elastic composite should have greater ductility and formability than a two-phase composite in which E and B are coupled by directly bonding two ceramic materials with no compliant matrix. A finite element analysis and homogenization of a representative volume element is performed to determine the effective electric, magnetic, mechanical, and coupled-field properties of an elastic (epoxy) matrix reinforced with piezoelectric and piezomagnetic fibers as functions of the phase volume fractions, the fiber (or particle) shapes, the fiber arrangements in the unit cell, and the fiber material properties with special emphasis on the symmetry properties of the fibers and the poling directions of the piezoelectric and piezomagnetic fibers. The effective magnetoelectric moduli of this three-phase composite are, however, less than the effective magnetoelectric coefficients of a two-phase piezoelectric/piezomagnetic composite, because the epoxy matrix is not stiff enough to transfer significant strains between the piezomagnetic and piezoelectric fibers.Item Micromechanics Modeling of Nonlinear and Time-dependent Responses of Piezoelectric 1-3, 0-3, and Hybrid Composites(2014-04-18) Lin, Chien-HongNonlinear electromechanical and polarization switching behaviors of piezoelectric materials and viscoelastic nature of polymers result in the overall nonlinear and hysteretic responses of active polymeric composites. Understanding the nonlinear behavior of the active polymeric composites is crucial in designing structures comprising of these active materials. This study presents three micromechanical models, i.e., fiber-, particle-, and hybrid-unit-cell models, to study the effective nonlinear and hysteretic electro-mechanical responses of 1-3, 0-3, and hybrid piezocomposites, respectively. The microstructures of the active composites are idealized with periodically distributed arrays of cubic representative unit cells. A unit cell is divided into several subcells. The fiber- and particle-unit-cell models consist of four and eight subcells, respectively. The hybrid-unit-cell model is derived based on the fiber-unit-cell model of 1-3 active composites consisting of fiber and matrix subcells, in which the matrix subcells are comprised of a particle-unit-cell model of 0-3 active composites. In order to obtain the overall nonlinear responses of the active composites linearized micromechanical relations are first used to provide trial solutions followed by iterative schemes in order to correct errors from linearizing the nonlinear responses. The micromechanical predictions are capable in predicting the overall nonlinear electromechanical, time-dependent, and polarization switching responses of active composites available in literature. Parametric studies are also performed to illustrate the effects of microstructural geometry and volume content of the piezoelectric inhomogeneities as well as loading history on the overall nonlinear and hysteretic responses of active composites. Finally, a multi-scale analysis of a functionally graded piezoelectric bimorph actuator using the developed particle-unit-cell model is given as an example of practical applications.Item Multifunctional Composites and Devices for Sensing and Energy Harvesting(2011-08-08) Cleveland, Michael AllenThis research investigates a novel class of active materials for energy and sensing applications. Magnetocaloric alloys, Gd5Si2Ge2, were developed into a composite with poly(vinylidine flouride) (PVDF), piezoelectric polymer. The giant megnetocaloric property combined with the piezoelectricity creates extraordinary properties for composite materials. The research approach was primarily experimental. Activities include synthesis, characterization, and device design and evaluation. Using the arc melting method, the magenetocaloric samples were created. Multi-length scales characterized using atomic force microscopy (AFM), optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-Ray diffraction (XRD), and X-Ray Photoelectron spectroscopy (XPS). The prototype devices were evaluated for their power generation and efficiency. Through those techniques, the fundamental understanding in the new materials was obtained. The relationships between process-microstructures, microstructure-properties, and structure-power generation were established. Results showed that the phase transformation of the magnetocaloric material at its Curie temperature induced a significant increase in power generation in the peizeoelectric polymer. Such transition was also beneficial for a laminated device for energy harvesting. In addition, it was found that the oxidation that occurred during high temperature melting stabilized the orthorhombic phase at room temperature. The multifunctional composites as well as the laminated structure use the thermal expansion of the magnetocaloric material for energy harvesting, cyclic monitoring, and/or thermal switching. This thesis consists of six chapters. Chapter I provides a history and explanation of the materials used. Chapter II provides an explanation of the motivation for this work. Chapter III addresses the experimental procedures. The results of which are presented in Chapter IV and discussed in Chapter V. The research is summarized and future recommendations are given in Chapter VI.Item Study of Thermo-Electro-Mechnical Coupling in Functionally Graded Metal-Ceramic Composites(2012-12-10) Doshi, Sukanya 1988-Piezoelectric actuators have been developed in various forms ranging from discrete layered composites to functionally graded composites. These composite actuators are usually made up of differentially poled piezoelectric ceramics. This study presents analyses of thermo-electro-mechanical response of piezoelectric actuators having combinations of metal and ceramic constituents with through thickness gradual variations of the metal and ceramic compositions. This is done in order to achieve better performance. The piezoelectric ceramic constituent allows for electro-mechanical coupling response and higher resistance to elevated temperatures while the metal constituent provides more ductile composites. The gradual variation in the ceramic and metal composition helps to avoid high stress concentrations at the layer interfaces in composites. A functionally graded composite is analyzed with discrete layers of piezoelectric ceramic/metal composite. Each layer in the functionally graded composite has a fixed ceramic/metal composition. The governing equation for such a piezoelectric functionally composite beam is presented based on a multi-layer Euler-Bernoulli beam model and the overall displacement response of the beam under thermal, mechanical and electrical stimuli is predicted. The variation of this response is studied with respect to functional grading parameter, number of layers, thermal and electrical and mechanical stimuli applied. It is found that the displacement due to thermal and mechanical effects can be mitigated to some extent by the application of an electric field. It is also observed that layers of varying thickness may be assumed to model the functional grading more accurately i.e. use thinner layers where the grading changes rapidly and thicker layers where the grading changes gradually. In addition to the above parametric studies, the change in the material properties with temperature is also studied. It is found that the temperature-dependent material parameters are important when the actuators are subjected to elevated temperatures.