Acoustic bubble-powered miniature rotor for wireless energy harvesting in a liquid medium

This paper presents a new type of acoustic energy harvesting technology in which a miniature rotor actuated by acoustically oscillating bubble-induced synthetic jets periodically vibrates piezocantilevers in order to generate electric power. The behavior of an oscillating bubble under acoustic excitation and an oscillating bubble-induced synthetic jet is experimentally verified to prove the working principle of an acoustically driven miniature rotor. The motion of the acoustically driven miniature rotor and the generated electric voltage from the vibrating piezocantilever are investigated. The rotating speed of the rotor and the electric voltage generated are highly dependent on the applied acoustic frequency. A custom-made electrical circuit with different electric loads is used to rectify the electric voltage and power generated by the vibrating piezocantilever. As proof of concept, storage capacitor charging tests are conducted with 0.1 μF and 1 μF capacitors. Furthermore, the effect of multiple piezocantilevers on the electric energy density is investigated to demonstrate the possibility of improving the electric energy density obtained from the proposed energy harvesting technology. The investigation shows that the total value of the voltage generated from piezocantilevers is proportional to the number of piezocantilevers.