Sound energy harvesting using a doubly coiled-up acoustic metamaterial cavity

A new sound energy harvesting system that comprises an acoustic metastructure and a double-clamped piezoelectric bimorph plate is presented. A subwavelength-scale acoustic metastructure is specially designed by utilizing a doubly coiled-up configuration for the strong confinement of the sound energy inside the acoustic metamaterial cavity in the low frequency range. The amplified sound pressure in the acoustic metamaterial cavity then substantially increases the vibratory motions of the piezoelectric bimorph plate. For the purpose of generating more electricity from the sound, the resonant frequency of the acoustic metamaterial cavity is tuned to the fundamental frequency of the piezoelectric bimorph plate. The numerical and experiment results show that the proposed sound energy harvesting system increase a sound pressure level (SPL) by up to ∼16 dB, and yields an output voltage that is 6.32 times higher than that of the conventional piezoelectric energy harvesting plate. For the incident SPL of 100 dB, the maximum output power is measured as approximately 0.345 μW at a resonant frequency of 600 Hz.