Experimentally tailoring acoustic topological edge states by selecting the boundary type

With the valley Hall effect, acoustic waves at a frequency in a new bandgap in the frequency spectrum opened by breaking the spatial symmetry of a unit cell in a particular metamaterial may propagate at the boundaries of the structure (edge state) or at the interface between two topologically different structures (interface state). In a previous study, we have numerically found that, when the acoustic wave propagates along the boundary of a single structure, the selection of the boundary type plays a decisive role in tailoring the frequency range covered by the edge state. We here experimentally verified the tailoring function of the different types of boundaries. In particular, it was shown that the attenuation of acoustic waves changes remarkably with the boundary type, which is of great significance in tailoring the propagation path. The present experimental study, along with our previous simulation results, provides solid guidance for the design of topological acoustic devices with diverse wave propagation paths.