Passive acoustic metasurfaces for high-efficiency wavefront transformations

Abstract

Metasurfaces have offered new degrees of freedom to control the propagation properties of acoustic waves. Gradient metasurfaces, first proposed in optics, and recently extended to acoustics, add an extra transverse momentum to the incident plane wave so that reflected and refracted waves can be rerouted without having to rely on conventional Snell’s Law. However, recent studies have shown that gradient metasurfaces cannot transfer all incident energy into the desired direction without causing unwanted parasitic diffraction and limiting the overall transformation efficiency. More sophisticated metasurface designs have considered impedance matching to address this issue, but this inherently requires the use of active and lossy materials for extreme wave transformations. In this talk, we present our recent efforts in designing passive acoustic metasurfaces with unitary efficiency in beam steering, even when considering extreme steering angles. We consider nonlocal surface impedance profiles and the use of bi...