Subwavelength acoustic topological edge states realized by zone folding and the role of boundaries selection
This article reports a realization of subwavelength acoustic topological edge states realized by a triangular array of hexagonal columns with Helmholtz resonators. Using the strategy of zone folding, Dirac cones can be folded into double Dirac cones to construct pseudo-spin states. By adjusting the length of both the center and corner units, topological phase transition as well as the common bulk bandgap can be achieved. The calculated results show that the acoustic metamaterials with different boundaries exhibit different bulk transmission properties. Topological acoustic metamaterials can be combined with different boundaries to construct nine different interfaces, and the simulation results show that nine different interfaces can exhibit robust, weak, and even disappearing topological edge states. We manufacture the samples and carry out experiments to test the transmission spectra of nine different interfaces. Experimental results demonstrate that a sound wave can transmit well along the topological interface 1 path compared with the other eight interface paths. This study provides a simple approach to create acoustic topological edge states at the subwavelength scale and experimentally confirms the influence of boundaries selection on acoustic topological insulators.