Switchable directional sound emission with improved field confinement based on topological insulators

Abstract

Directional sound emission and reception are important in many practical applications, such as acoustic imaging, communications, and structural health monitoring. In this Letter, we propose and demonstrate an acoustic antenna for realizing switchable directional sound emission with improved field confinement. We construct the antennas with two rotatable phononic crystals to form different zigzag and armchair interfaces, then numerically and experimentally investigate their radiation performance. The simulated and measured sound pressure fields are in good agreement, which shows that the valley-projected edge states are excited with angular selectivity at the interfaces and then directionally radiate in different directions for different interfaces. In addition, the far-field radiation patterns of the proposed antennas clearly illustrate improved confinement of acoustic energy along the radiation directions, which can be attributed to the double C3 symmetry of the snowflake-like scatterers employed to construct the antennas. Our proposed antenna greatly enriches the functionalities of topological insulators and provides a practical method to design acoustic devices with switchable and improved directional emission.