Anomalous reflection and vortex beam generation by multi-bit coding acoustic metasurfaces

Coding metasurfaces can combine simple logical bits to acquire sophisticated functions in wave control. Recently, coding metasurfaces have been demonstrated to take flexible control of the acoustic wave and realize intriguing functionalities such as wave branching, Fresnel lens, and asymmetric transmission. However, the previous design contains only two coding units, and thus, the resultant functions are relatively limited. Here, we propose the multi-bit coding acoustic metasurfaces to manipulate the reflection of acoustic waves. Theoretical predictions and experimental results are given to demonstrate the functions of wave branching and acoustic directionally propagating. We further perform digital convolution operations on the 3-bit coding metasurfaces and realize the generation and manipulation of an acoustic vortex beam. The presented design provides a flexible way for manipulating reflected acoustic waves and may find applications in construction engineering and particle trapping.