Broadband Controllable Asymmetric Accelerating Beam via Bilayer Binary Acoustic Metasurfaces

Abstract In this work, asymmetric accelerating beam is achieved numerically and experimentally by taking advantage of a bilayer binary acoustic metasurface (BAM) composed of the rectangular cavity (bit ‘0’) and the waveguide with seven Helmholtz resonators (bit ‘1’). The fundamental physical mechanism is based on the different phase modulations induced from both sides of the structure because the left and right layers can be regarded as an angle‐selective refractor and an accelerating beam generator, respectively. The presented structure can work in a wide range of 5000–6000 Hz and switch from unidirectional to bidirectional transmission conveniently by altering the air gap between the two composing layers. Furthermore, asymmetric self‐focusing in a broadband is able to be realized as well by utilizing two symmetrical bilayer BAMs, which enriches the functionality of the design. Compared with previous asymmetric transmission devices, the authors' approach has the advantages of simple design, broadband multifunctionality, and tunable property, which may have promising applications in numerous acoustic fields including biomedical engineering, nondestructive testing, and acoustic communication.