Energy Harvesting with Piezoelectric Element Using Vibroacoustic Coupling Phenomenon

This paper describes the vibroacoustic coupling between the structural vibrations and internal sound fields of thin structures. In this study, a cylindrical structure with thin end plates is subjected to the harmonic point force at one end plate or both end plates, and a natural frequency of the end plates is selected as the forcing frequency. The resulting vibroacoustic coupling is then analyzed theoretically and experimentally by considering the dynamic behavior of the plates and the acoustic characteristics of the internal sound field as a function of the cylinder length. The length and phase difference between the plate vibrations, which maximize the sound pressure level inside the cavity, are clarified theoretically. The theoretical results are validated experimentally through an excitation experiment using an experimental apparatus that emulates the analytical model. Moreover, the electricity generation experiment verifies that sufficient vibroacoustic coupling can be created for the adopted electricity generating system to be effective as an electric energy-harvesting device. 1. Introduction Recently, scavenging ambient vibration energy and converting it into usable electric energy via piezoelectric materials have attracted considerable attention [1]. Typical energy harvesters adopt a simple cantilever configuration to generate electric energy via piezoelectric materials, which are attached to or embedded in vibrational elements. High-amplitude excitations reduce the fatigue life of these harvesters. Thus, placing appropriate constraints on the amplitudes is one of significant ways to improve the performance of harvesters. A cantilever beam, whose deflection was constrained by a bump stop, was modeled. The effect of electromechanical coupling was estimated in a parametric study, where the placement of the bump stop and the gap between the beam and stop were chosen as parameters [2]. Acoustic energy as well as vibration energy to be harvested sufficiently fills our working environment. Thermoacoustic engines that exploit the inherently efficient Stirling cycle and are designed on the basis of a simple acoustic apparatus with no moving parts have been regarded as the representative means for harvesting acoustic energy [3]. As an example application, electricity generation using resonance phenomena in a thermoacoustic engine was investigated with aim of harvesting the work done in the engine. The acoustic energy spent on electricity generation was harvested from a resonance tube branching out of the engine, and the appropriate position of the