Customizable and tunable acoustic topology metasurfaces with high-efficiency anomalous reflection/refraction

The invention of metasurfaces provides an unprecedented opportunity for efficiently manipulating the wavefront of acoustic devices. However, most of the design strategies, which rely on the generalized Snell’s law, overlook the coupling effects among adjacent cells of metasurface. This oversight results in low-efficiency wavefront manipulations at large angles. Furthermore, the inherent limitations of the generalized Snell’s law significantly impede the advancement of tunable metasurfaces. To address these challenges, we propose a novel non-local acoustic metasurface topology optimization framework with the aim of achieving high-efficient, tunable acoustic wave manipulations. In this paper, we successfully implement a customized metasurface design by utilizing non-local coupling interactions within the metasurface and employing a gradient-free topology optimization algorithm. This approach allows us to surpass the theoretical efficiency limitation of the generalized Snell’s law. We achieve over 95% efficiency, even for large angle anomalous reflection/refraction. Additionally, we introduce a tunable method for metasurface based on a soft-substrate. This mechanism enables efficient tunable design of acoustic metasurfaces with large angles by utilizing the reversible large deformation capability of soft materials to adjust the coupling within the metasurface. It breaks the fundamental limitation of conventional designs that solely rely on gradient phase. Since soft-substrate metasurfaces can easily adapt to irregular surface shapes of objects, the proposed mechanism opens up possibilities for designing flexible and tunable metasurfaces.