Compact topological waveguide for acoustic enhanced directional radiation

Enhanced directional radiation is important for various applications such as lasers and antennas. However, almost all existing enhanced directional emitters rely on the use of materials or structures that provide multiple reflections, which are often bulky, lossy, and difficult to fabricate. Here, we theoretically propose and experimentally demonstrate acoustic enhanced directional radiation with topological interface states in a specially designed acoustic waveguide with subwavelength width and no additional structure for multiple reflections. This waveguide is an acoustic analog of the double Su–Schrieffer–Heeger chain, in which a topological bandgap can be created by opening degenerate points away from the boundary of the Brillouin zone. Topological interface states between two topologically different waveguides were experimentally observed. A leaky-wave design is proposed for acoustic enhanced directional radiation. This leaky-wave waveguide can improve the radiation resistance and efficiency of a point source, and the radiation direction is locked by the momentum of the degenerate points. Acoustic enhanced directional radiation with more than ten times energy enhancement is observed in the experiment. The proposed strategy shows potential in the subwavelength wave manipulation and can be applied to acoustic communication, nondestructive evaluation, and biomedical imaging.