High-efficiency Ultrathin Nonlocal Waterborne Acoustic Metasurface

High-performance and lightweight waterborne acoustic devices have provided important support for the development of ocean exploration, health monitoring, etc. In this work, we propose a high-efficiency ultrathin nonlocal waterborne acoustic metasurface. Due to strong nonlocal interaction between the waterborne unit cells induced by the fluid-solid interaction, a nonlocal design concept based on diffraction theory and the optimization approach is proposed to design waterborne acoustic metasurfaces, in contrast to the local design based on the generalized Snell's law. The theoretical efficiency limitation of the generalized Snell's law can be broken, and unitary efficiency could be obtained even for large-angle anomalous reflection. The high-efficiency modulation is achieved owing to the energy flow along the metasurface resulting from the nonlocal interaction. The thickness of the waterborne acoustic metasurface can be minimized to one tenth or even one sixtieth of the working wavelength. The nonlocal design with fluid-solid interaction paves the way for high-efficiency and deep-subwavelength waterborne acoustic wave manipulation.