Low frequency acoustic energy harvester based on a planar Helmholtz resonator

A novel acoustic energy harvester (AEH) based on an acoustic Helmholtz resonator is proposed in this research to harvest low frequency acoustic energy. The height of the resonator is deep subwavelength of the interesting sound wave, meaning that the overall structure is compact. The neck component is designed as tapered form, specifically to reduce the influence of acoustic resistance. The proposed Helmholtz resonator was evaluated using numerical simulation and experimental tests. In the comparison experiment, the proposed acoustic resonator is compared with an acoustic resonator with uniform neck configuration, and the measured results show the proposed structure can amplify low frequency sound effectively and the resonance frequency corresponds well with the numerical simulation. A PZT-5H piezoelectric patch, bonded to the top side of the AEH, is used to convert mechanical strain energy into electrical power. Experimental results illustrate that under 100 dB SPL excitation, maximum 27.2 μW power can be harvested at 217 Hz and maximum 64.4 μW power can be harvested at 341 Hz. These results correspond to acoustic and mechanical resonance respectively.