Multi-band acoustic topological insulator

Abstract

As an analog of topological insulators in acoustics, acoustic topological insulators possess the pseudospin-dependent one-way transmission of sound edge states immune to scattering, and have potential applications in acoustic detection, sensing and communication. Achieving multiple working frequency bands or widening the bandwidth of a single working frequency band is a critical goal for any application. However, the realization of existing acoustic topological insulators requires the construction of a double Dirac cone at the center of the Brillouin zone, which poses a challenge to realize multi-band topological edge states and greatly impedes the application of acoustic topological insulators. To this end, this paper proposes a general method for constructing multi-band acoustic topological insulators by the lattice superposition mechanism. Considering the double degenerate points appearing in pairs at the center of the Brillouin zone, we showed that tuning the coupling strength of structure and sound field, the characteristics of the double degenerate points with unique modal features in different lattices could be obtained. Using the lattice superposition mechanism, we demonstrated that the multiple pairs of degeneracy points with different modal features could be realized at the center of the Brillouin zone. Multi-band topologically protected edge states and topological one-way sound transport were further demonstrated by simulation and experimental results. In addition, according to the offset effect of the edge states, we discovered the phenomenon of band separation for edge states on the same interface, which could realize the frequency-selective characteristic of edge states. These results provide a general approach for the design and realization of multi-band acoustic topological insulators.