Switchable asymmetric acoustic transmission based on topological insulator and metasurfaces

Dynamically switching the symmetric and asymmetric acoustic transmission (AAT) is significant in sound manipulation. In this paper, we present the design of switchable AAT in a certain frequency band, which is composed of an acoustic valley hall (AVH) topological insulator and acoustic metasurface (AMS). The underlying mechanism of AAT is attributed to the valley-selective excitation of AVH edge modes and the arbitrary refraction angle controls of the AMS. The acoustic transmission can only occur when the AVH edge modes are excited by controlling the direction of the incident sound waves with the help of AMS. By moving the AMS, the device can shift from symmetric transmission to asymmetric transmission within the designed frequency band. Importantly, the acoustic transmission through the device is topologically protected, which is robust to bends and defects. The AMS based on the spiral-coiling structure is chosen to reach a high acoustic transmission. The performance of switchable AAT is validated with full-wave simulations. Our work may open a new method for introducing the advantages of topological insulators to AAT.