Areconfigurable coding acoustic metasurface for multifunctional beam manipulation.

The advent of reconfigurable metasurfaces incorporating active elements offers the flexibility of engineering acoustic waves with external behaviors, but it still remains challenging to reduce the complexity of design while ensuring a subwavelength thickness and wide operating band. Here we theoretically design and experimentally realize a reconfigurable coding acoustic metasurface composed of compact unit cells (subwavelength reconfigurable elements, H = 18 mm) that enable dynamic wavefront shaping across a broad frequency range (1.7-2.5 kHz).In our design, each individual unit cell of metasurface has a coiled configuration that can be divided into two types of encoding units: 0 and 1, by only changing a single structural parameter of the internal crossbar. In particular, the unit cell has a deep-subwavelength scale and a broad operating bandwidth, which enables precise wavefront manipulations and simple reconfiguration strategies. The multi-functional performance of our scheme is numerically and experimentally verified via the demonstration of two distinctive examples of beam splitting and acoustic focusing. Both the simulated and measured results agree well with the theoretical predictions, showing the designed coding metasurface efficiently and flexibly manipulates the wavefront of the outcoming waves to form the desired specific patterns. With advantages in terms of easy fabrication, ultrathin thickness and broad bandwidth, our design opens route to the design of novel acoustic functional devices based on active space-coiling metasurfaces and holds significant application potential in diverse fields such as acoustic imaging and communication, etc.