Biphysical coding metasurfaces for independent and continuous manipulations of electromagnetic and acoustic waves

It still remains a significant challenge using the current technology to fabricate devices with customized functions for both electromagnetic (EM) and acoustic waves since the demand of biphysical manipulation, which means that the same device can be used to control EM and acoustic waves simultaneously, difficult is to satisfy in nature. However, the emergence of metasurfaces provides a new way to synchronously control the propagation for both waves. Unfortunately, the independent and continuous wavefront manipulation of multiple physical fields, including acoustic and EM waves, still requires overcoming significant challenges. In this study, we propose and demonstrate EM-acoustic biphysical coding metasurfaces (BCM) which are capable of independently engineering propagation behaviours for both waves. In addition, continuous phase tunability across each domain can be attained. Eight kinds of unit cells with different geometrical parameters which consist of dual-layers are employed to serve as 2-bit reflection-type meta-atoms, thus offering opportunities for almost arbitrary wavefront manipulation of EM and acoustic waves as desired. The simulation results demonstrate that the proposed BCM can perform different functionalities for dual waves, such as multiple-beam generation, focusing, and vortex beam generation, which can be flexibly switched by tuning coding sequences of unit cells. The research results can help to enrich functions of metasurfaces, expand their application scope, and pave the way for the development of biphysical multifunctional devices and applications in the future.