Additive manufacturing of channeled acoustic topological insulators.

We propose and fabricate an acoustic topological insulator to channel sound along statically reconfigurable pathways. The proposed topological insulator exploits additive manufacturing to create unit cells with complex geometry designed to introduce topological behavior while reducing attenuation. We break spatial symmetry in a hexagonal honeycomb lattice structure composed of a unit cell with two rounded cylindrical chambers by altering the volume of each chamber, and thus, observe the quantum valley Hall effect when the Dirac cone at the K-point lifts to form a topologically protected bandgap. Moderately protected edge states arise at the boundary between two regions with opposite orientations. The resulting propagation of a topologically protected wave along the interface is predicted computationally and validated experimentally. This represents a first step towards creating reconfigurable, airborne topological insulators that can lead to promising applications, such as four-dimensional sound projection, acoustic filtering devices, or multiplexing in harsh environments.