Tunable acoustic energy harvester using Helmholtz resonator and dual piezoelectric cantilever beams

A tunable acoustic energy harvester consisting of dual piezoelectric cantilever beams and a Helmholtz resonator with a perforated backplate is proposed. The tunability of the operation frequency band can be achieved not only via simply adjusting the radius (r) of the aperture due to the strong dependence of resonance frequencies of the Helmholtz resonator on the acoustic impedance affected by r, but also by changing the distance (d) between piezoelectric cantilever beams because of their magnetic force interaction. Experimental results show that as r (or d) increases from 0 (or 1.4) to 1.0 (or 3.4) cm, the frequency band is broadened and varies from 175.5∼198 (or 175.5∼213) Hz to 170.5∼221 (or 161∼203) Hz. The average ratio of the adjusted frequency bandwidth to r (or d) can reach 28 (or 2.25) Hz/cm over the range of 125∼250 Hz.