Onset of Self-Excited Oscillations of Traveling Wave Thermo-Acoustic-Piezoelectric Energy Harvester Using Root-Locus Analysis

The onset of self-excited oscillations is developed theoretically for a traveling wave thermo-acoustic-piezoelectric (TAP) energy harvester. The harvester is intended for converting thermal energy, such as solar or waste heat energy, directly into electrical energy without the need for any moving components. The thermal energy is utilized to generate a steep temperature gradient along a porous regenerator. At a specific threshold of the temperature gradient, self-sustained acoustic waves are generated inside an acoustic resonator. The resulting pressure fluctuations excite a piezoelectric diaphragm, placed at the end of the resonator, which converts the acoustic energy directly into electrical energy. The pressure pulsations are amplified by using an acoustic feedback loop which introduces appropriate phasing that make the pulsations take the form of traveling waves. Such traveling waves render the engine to be inherently reversible and thus highly efficient. The behavior of this class of harvesters is modeled using the lumped-parameter approach. The developed model is a multifield model which combines the descriptions of the acoustic resonator, feedback loop, and the regenerator with the characteristics of the piezoelectric diaphragm. A new method is proposed here to analyze the onset of selfsustained oscillations of the traveling wave engine using the classical control theory. The predictions of the developed models are validated against published results. Such models present invaluable tools for the design of efficient TAP energy harvesters and engines

Energy Harvester with a Dynamic Magnifier

Conventional energy harvester typically consists of a piezoelectric element, which is sandwiched between a proof mass and a base subjected to sinusoidal excitation. The resulting relative motion between the proof mass and the base produces a mechanical strain in the piezoelectric element, which is converted into electrical power by virtue of the direct piezoelectric effect. In this study, harvester is provided with a dynamic magnifier consisting of a spring-mass system which is placed between the piezoelectric element and the moving base. The main function of the dynamic magnifier, as the name implies, is to magnify the strain experienced by the piezo-element in order to amplify the electrical power output of the harvester. With proper selection of the design parameters of the magnifier, the harvested power can be dramatically enhanced and the effective bandwidth of the harvester can be improved. The theory governing the operation of this class of energy harvesters with dynamic magnifier (EHDM) is developed using the Lagrangian dynamics approach. Numerical examples are presented to illustrate the performance characteristics of the EHDM in comparison with the conventional energy harvesters. The obtained results demonstrate the feasibility of the EHDM as a simple and effective means for enhancing the magnitude and spectral characteristics of conventional harvesters. </jats:p

Onset of Self-Excited Oscillations of Traveling Wave Thermo-Acoustic-Piezoelectric Energy Harvester

The onset of self-excited oscillations is developed theoretically for a traveling wave thermo-acoustic-piezoelectric (TAP) energy harvester. The harvester is intended for converting thermal energy, such as solar or waste heat energy, directly into electrical energy without the need for any moving components. The thermal energy is utilized to generate a steep temperature gradient along a porous stack. At a specific threshold of the temperature gradient, self-sustained acoustic waves are generated inside an acoustic resonator. The resulting pressure fluctuations excite a piezoelectric diaphragm, placed at the end of the resonator, which converts the acoustic energy directly into electrical energy. The pressure pulsations are amplified by using an acoustic feedback loop which introduces appropriate phasing that make the pulsations take the form of traveling waves. Such traveling waves render the harvester to be inherently reversible and thus highly efficient. The behavior of this class of harvesters is modeled using the lumped-parameter approach. The developed model is a multi-field model which combines the descriptions of the acoustic resonator, feedback loop, and the stack with the characteristics of the piezoelectric diaphragm. A new method is proposed here to analyze the onset of self-sustained oscillations of the traveling wave engine using the classical control theory. The predictions of the developed models are validated against published results. Such models present invaluable tools for the design of efficient thermo-acoustic-piezoelectric (TAP) energy harvesters and engines.</jats:p

Impact and Bandgap Characteristics of Periodic Rods With Viscoelastic Inserts and Local Resonators

Abstract A comprehensive theoretical and experimental study is presented of the bandgap behavior of periodic viscoelastic material (VEM) composites subjected to impact loading. The composites under consideration consist of an assembly of aluminum sections integrated with periodic inserts which are arranged in one-dimensional configurations. The investigated inserts are manufactured either from VEM only or VEM with local resonators (LR). A finite element model (FEM) is developed to predict the dynamics of this class of VEM composites by integrating the dynamics of the solid aluminum sections with those of VEM using the Golla-Hughes-Mctavish (GHM) mini-oscillator approach. The integrated model enables, for the first time, the accurate predictions of the bandgap characteristics of periodic viscoelastic composites unlike previous studies where the viscoelastic damping is modeled using the complex modulus approach with storage modulus and loss factor are assumed constants and independent of the frequency or the unrealistic and physically inaccurate Kelvin–Voigt viscous-damping models. The predictions of the developed FEM are validated against the predictions of the commercial finite element package ansys. Furthermore, the FEM predictions are checked experimentally using prototypes of the VEM composites with VEM and VEM/LR inserts. Comparisons are also established against the behavior of plain aluminum rods in an attempt to demonstrate the effectiveness of the proposed class of composites in mitigation of the structural response under impact loading. Close agreements are demonstrated between the theoretical predictions and the obtained experimental results.</jats:p