Tunable Acoustic Metasurface for Three-Dimensional Wave Manipulations

Acoustic metasurfaces display unprecedented potential for their unique and flexible capabilities of wave front manipulations. Although rapid progress and significant developments have been achieved in this field, it still remains a significant challenge to obtain an acoustic metasurface that can perform different functions in three-dimensional (3D) space, as desired. Here, a tunable acoustic metasurface composed of Helmholtz-resonator-like digital-coding meta-atoms is presented to overcome the limitation and realize 3D dynamic wave manipulations. The digital meta-atom is constructed from two cylindrical cavities controlled by a motor. By changing the depth of the bottom cavity with the motor automatically, the reflection phase of the meta-atom can be adjusted continuously over the range of nearly 360\ifmmode^\circ\else\textdegree\fi{}, realizing the required digital states. To build the relationship between the digital-coding profiles and scattering patterns, convolution and addition operations are implemented. Based on such operations, various fascinating functionalities, such as arbitrary scattering-pattern shift and superposition of different scattering beams, are achieved. This study paves the way for studying acoustic metasurfaces from the digital perspective and provides efficient methods for realizing spatial acoustic wave control.