Journal Article topological insulators Majorana bound states acoustic antennas acoustic communication acoustic metamaterials contactless rotation deep-subwavelength acoustic imaging higher‐order topological insulator hyperbolic polaritons mechanical metamaterials meta engine blocks metamaterials mode-frequency-division multiplexing momentum twisting multiplexing technology non‐Hermitian topological insulator phononic crystals polaritons second-order topological insulators spatiotemporal metasurface spoof surface acoustic waves superdirectivity topological acoustics topological corner states topological edge states topological metamaterials ultrasonic motors valley-Hall phase van der Waals materials