Acoustic metasurface by layered concentric structures

Metasurface-based acoustic wave-front manipulation with broad bandwidth and low transmission loss shows great significance in high-intensity applications such as ultrasonic therapy, acoustic tweezers, and haptics. By taking advantage of the helical-structured metamaterials and their concentrically layered arrangement, we present a systematic strategy to construct two-dimensional transmissive acoustic metasurfaces that possess matched impedance to the background medium and simple governing parameters. As a proof of concept, a concentrically layered circular metalens supporting conversion from spherical wave to plane wave is designed and experimentally demonstrated. It is capable of operating in more than one octave band with high transmission. This work could inspire more intriguing and flexible designs in three-dimensional wave control, which may enhance the practicality of acoustic metasurfaces.