2aSA9. Harvesting ambient acoustic energy using acoustic resonators Bin Li and Jeong H. You*

Sound is abundant in our everyday life, especially in urban environments. Despite the prevalence of sound, it is difficultto harvest acoustic energy in practical applications due to its low power density. In this study, we conduct numerical calculations to maximize the stored energy in piezoelectric beam arrays placed inside a Helmholtz resonator. The shape ofthe Helmholtz resonator is optimized to be a tube in order to increase the sound pressure amplification factor and lowerthe eigenfrequency to ~400 Hz. When the tube resonates by an external sound, the piezoelectric beams vibrate by ampli-fied standing wave resulting in generating electrical energy. The simulation results show that a single beam is able to store~0.0569 μJ strain energy when it is placed near the tube inlet with the incident sound pressure level of 100 dB. Using nine piezoelectric beams increases the total strain energy to 0.382 μJ

Due to its prevalence in urban environments, acoustic energy has become very attractive as a possible energy resource to harvest. A big challenge in harvesting acoustic energy comes from its low power density. A previous study reported that the acoustic power density is 0.03W/cm3 and 0.96 W/cm3with incident sound pressure levels (SPL) of 75 dB and 100 dB, respectively [1]. Liu et al. [2-3] developed an electromechanical Helmholtz resonator using a piezoelectric backplate, and the output power of 30 mW was obtained from the incident SPL of 160 dB. Wu et al. [4-5] placed the piezoelectric polyvinglidene fluoride (PVDF) beam in sonic crystals and the output power of ~35 nW was obtained. In this work, multiple piezoelectric beams have been placed inside an acoustic resonator so that the resonant acoustic wave drives the vibration of piezoelectric beam resulting in electricity generation. To increase the sound pressure amplification at resonance, the shape of the resonator has been chosen to be a straight tube with its eigenfrequency around 400 Hz. Displacements and mechanical energy stored in the piezoelectric beams have been studied numerically, and the effect of spacing between beams is presented.

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