Efficient conversion of waterborne acoustic waves into electrical energy by using the phase-reversal Fresnel zone plate.

Acoustic energy harvesting assisted by metamaterial devices, deemed as a promising way of utilizing green energy, has been extensively investigated in the science and engineering communities during the past years, considering the ubiquitous sound waves in nature. To date, one of the biggest challenges in the acoustic energy harvesting lies in the improvement of efficiency and output power. In this work, we propose to use the phase reversal Fresnel zone plate (PR-FZP) for efficient acoustic energy harvesting in aquatic environment instead of using the traditional FZP. We first show in simulations that the PR-FZP generates a focusing with much larger intensity than traditional FZP at different operation frequencies and focal lengths. Then we conduct experiments and demonstrate a 141% enhancement in output power of the piezo-receiver by using PR-FZP, in comparison to the FZP case. Here the capacitor charging tests show a 162.5% enhancement in the average charging rate and a 249.3% enhancement in average charging power, in contrast to the FZP case. With the harvested acoustic energy stored in the battery, we can drive a propeller to rotate which can further induce motion underwater. Our research has significant implications for the development of sound-driven devices with versatile functionalities.