An efficient low-frequency acoustic energy harvester

Here, an efficient acoustic energy harvester is proposed that is suitable for low-frequency bands. It is composed of a tunable Helmholtz resonator with a flexible bottom, with affixed piezo disk and proof mass. The proof mass can lower the mechanical resonance frequency of the bottom, while increasing the harvested sound power. The proposed Helmholtz resonator was designed for sound pressure amplification. Furthermore, it is tunable, enabling adjustment of the acoustic resonance frequency to the mechanical resonance frequency. The designed tunable Helmholtz resonator has been fabricated and its function was experimentally verified. Furthermore, the acoustic energy harvesting study was conducted under 100 dB sound pressure level excitation. Experimental results show that the proposed harvester can generate 3.49 μW (at optimal load) when both resonance frequencies are matched, and the energy conversion efficiency can reach up to 38.4%.