Low frequency acoustic energy harvesting

A novel and practical acoustic energy harvesting mechanism to harvest a travelling sound at a low audible frequency (180 ~ 200Hz) is developed and studied both experimentally and numerically. The acoustic energy harvester in this study consists of a quarter-wavelength straight tube resonator and multiple piezoelectric cantilever plates placed inside the tube. When the tube resonator is excited by an incident sound at its acoustic resonant frequency, the amplified acoustic pressure inside the tube drives the vibration motions of piezoelectric plates, resulting in generating electricity. To increase the total voltage and power, multiple piezoelectric plates have been placed inside the tube. It has been found more beneficial to place the piezoelectric plates in the first half of the tube rather than in the entire tube. Installing multiple piezoelectric plates in the first half of the tube resonator modifies the acoustic resonant frequency and impedance. The influence of the presence of multiple piezoelectric plates on the accumulated acoustic power and harvesting efficiency of the harvester has been investigated.;In order to realize an AC/DC conversion in the acoustic energy harvester, the effect of external circuits has been investigated both numerically and experimentally. The external circuits in this study include a standard circuit, a conventional synchronized switch harvesting on inductor (SSHI) circuit, and self-powered SSHI circuits. Generally, conventional SSHI circuits have been commonly used, but the requirements of displacement sensors and an external power supply have severely limited their practical applications. In the acoustic energy harvester, it is also difficult to put a displacement sensor due to the space limit inside the tube resonator. Therefore, self-powered SSHI circuits which can operate without any displacement sensor and external power supply have been proposed and investigated. In our study, the maximum output power of self-powered S-SSHI is measured as 10.129 mW when the incident sound pressure level is 112 dB. The corresponding volume and areal power densities are at least one order higher than the previous acoustic energy harvesters.