The generation of acoustic Airy beam with selective band based on binary metasurfaces: Customized on demand

In this work, we present a type of binary metasurface (BM) to generate an acoustic Airy beam in air. Two coding bits, a rectangular cavity (bit "0") and a waveguide with seven Helmholtz resonators (bit "1"), are adopted to construct the acoustic structure, which offers degrees of freedom to manipulate the transmitted field. The operating band is capable of customizing in an ultrabroadband of 3000-15 000 Hz owing to the linear-like phase shift and high transmittance of the coding bits. To verify the feasibility of the design, a BM with a certain parameter (w = 5) is fabricated with photosensitive resin via stereolithography, and the working band is customized as 4000-5500 Hz. The experiment results show that the apparent self-bending beam is able to be generated in a broadband, which agree well with the numerical simulation. In addition, we further demonstrate that self-focusing can be realized by taking advantage of two symmetrical BMs conveniently, which improve the functionality of the coding bits. These results may provide potential application in biomedical ultrasound and nondestructive testing.