Bianisotropic Acoustic Metasurface for Surface-Wave-Enhanced Wavefront Transformation

Acoustic metasurfaces offer remarkable control of wave transmission and reflection, but with limited power efficiency in traditional systems. Perfect wavefront transformation with perfect efficiency traditionally requires either nonreciprocal or nonlocal responses, which are challenging to implement with passive designs. This study uses the automatically excited surface waves to design impedance-based acoustic metasurfaces requiring only reciprocal and local responses; thus passive structures suffice. Counterintuitively, transmission-type metasurfaces require nonzero reflected fields for maximum efficiency, and reflection-type metasurfaces need nonzero transmitted fields.