Perfect anomalous reflection and refraction with binary acoustic metasurfaces

Binary acoustic metasurfaces (AMs) are proposed and demonstrated with the goal of perfect anomalous reflection and refraction. The AMs require only two subunits per period, thereby greatly improving the fabrication accuracy and reducing the design process. Theoretical analysis gives the range of incident and diffracted angles for the case of only two propagating modes, one of which can be suppressed by designing the two subunits to have opposite phases, thereby achieving perfect anomalous reflection/refraction. Moreover, the reflection- and refraction-type binary AMs are realized using two types of space-coiling structures. Finite-element simulations show the realization of anomalous reflection and refraction, the energy efficiencies of which can reach almost 100%. The present work provides a simple and straightforward way to design high-efficiency and practical AMs that enable nearly ideal manipulation of reflected/transmitted waves.