Dual-band piezoelectric acoustic energy harvesting by structural and local resonances of Helmholtz metamaterial

The current study on acoustic energy harvesting is based on a single-band vibroacoustic conversion performed by either structural resonance or local resonance. In this paper, we propose a Helmholtz acoustic metamaterial (HAM) piezoelectric device having dual-band acoustic energy harvesting characteristics. The Helmholtz resonator of the metamaterial amplifies both structural and local resonances. HAM is designed based on the Bloch theorem, plane wave expansion method, and electroacoustic impedance analogy. Numerical simulation is performed to show the sound pressure amplification effect of HAM. A piezoelectric disk is bonded on the point defect of the Helmholtz metamaterial for energy localization and conversion, and HAM is clamped on a self-made experimental platform by simply supported boundary conditions on four sides. The time–frequency image of the voltage output from the swept frequency experiment shows two distinct bands corresponding to the structural resonance frequency of 381 Hz with the band width of 45 Hz and the local resonance frequency of 1526 Hz with the band width of 290 Hz. The peak-to-peak power of HAM is 0.13 mW, and its peak-to-peak voltage is 3.2 V at 391 Hz with the sound pressure of 31 Pa. At the input sound pressure of 23.32 Pa and frequency of 1526 Hz, the output voltage and power are found to be 1.5 V and 0.11 mW, respectively. Under the same amplitude of the input sound pressure, the output power of HAM is found 12.7 times and 4.4 times higher than those of the traditional acoustic metamaterial in the structural and local resonance bands, respectively. Field tests validate the superiority of the designed structure. In the milling environment, the voltage–pressure transmission rate reaches 0.11 V/Pa. The acoustic energy wall composed of HAM will be capable to provide a power solution for an intelligent factory.