Stepped acoustic metasurface with simultaneous modulations of phase and amplitude

Conventional acoustic metasurfaces (AMs) are limited in their ability to modulate phase and amplitude simultaneously. In this work, we analyze this limitation by using an effective medium model and propose a kind of full-control AM based on the model, which might give a more general method to build a full-control AM. The used unit is one segment of conventional space-coiling structure with adjustable height as a new degree of freedom. The metasurface can simultaneously modulate phase and amplitude for both transmitted and reflected acoustic waves. We demonstrate the abnormal refraction/reflection, acoustic focusing, and illusion effects by the metasurface.