Bianisotropic acoustic metasurfaces for wavefront transformation

Abstract

Acoustic metasurfaces are thin, engineered structures that can control the local reflection and transmission phase of acoustic waves, and thus enable a high degree of flexibility for wave manipulation. Here, we describe our recent work on so-called perfect metasurfaces, in which elements are designed that can control the local transmission and reflection amplitude and phase response of the metasurface. Controlling both the amplitude and the resulting asymmetric phase response requires a fundamentally asymmetric surface impedance for the unit cells. The resulting ideal surface properties thus have strong links to the concept of bianisotropy in electromagnetics and Willis coupling in elastodynamics. We have developed a shunt resonator-based element design that contains the needed degrees of freedom to independently control the surface impedance on both sides of the metasurface. Using this perfect metasurface design approach, we demonstrate the design and experimentally measurement of high efficiency wide-angle transmissive beam steering at levels beyond what is possible with phase control alone.