Bifunctional coding metasurfaces for acoustic wave manipulations

We present frequency-selective 1-bit bifunctional coding metasurfaces (BCMs) for acoustic-wave field manipulations. Unlike most conventional metasurfaces operating at a single frequency and having only one functionality, the BCM demonstrates the capability to achieve different functionalities at two distinct frequencies. The underlying mechanism is based on the design of the coding units with Helmholtz resonators operating at two frequencies independently. We demonstrate the achievement of different functionalities by the BCMs, involving acoustic focusing, generation of Airy beam, and acoustic splitting. The results are shown through theoretical predictions and finite-element simulations, which show good correspondence. Our work presents a promising metasurface design for pragmatic applications, such as multiple acoustic beam shaping and information preservation.