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Acoustic energy harvesting by piezoelectric curved beams in the cavity of a sonic crystal is investigated. A resonant cavity of the sonic crystal is used to localize the acoustic wave as the acoustic waves are incident into the sonic crystal at the resonant frequency. The piezoelectric curved beam is placed in the resonant cavity and vibrated by the acoustic wave. The energy harvesting can be achieved as the acoustic waves are incident at the resonant frequency. A model for energy harvesting of the piezoelectric curved beam is also developed to predict the output voltage and power of the energy harvesting. The experimental results are compared with the theoretical.

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By calculating the transmission coefficients by finite-element software, the study of the tunable acoustic band gap for two-dimensional (2D) phononic crystals composed of a square array of hollow cylinders in an air background is considered. The inclusions are a dielectric elastomer cylindrical actuator, which is made of a hollow cylinder sandwiched between two compliant electrodes. By applying a voltage between the compliant electrodes, the radial strain of the silicone-made actuator is investigated. The acoustic band gaps are changed due to the radial strain of the dielectric elastomer. The frequency range of the dielectric elastomer composite can be extended by increasing the applied voltage. A tunable acoustic band gap of the phononic crystal is realized via the unique character of dielectric elastomer.The calculations also demonstrate that there exists a local stop band within the pass band. With a local stop band gap, 2D phononic crystals may thus serve as an acoustic filter or switch.