Controllable and multi-band acoustic metamaterial topological insulators

The valley degrees of freedom, representing quantum states of energy extremes in momentum space, are introduced into the acoustic system, and the valley topological insulator analogs of the quantum valley Hall effect can control the sound wave to observe topological valley transport against backscattering in domain walls of different valley topological phase structures. However, most of the earlier acoustic topological insulators are based on Bragg scattering and topological states only work in a single frequency band, which limits the design of applications for multiband communications. Here, we propose multiband acoustic valley Hall topological metamaterials based on weak interaction of local resonance subunits with isolated modulation. Valley topological phase transitions exists at two separated frequency bands by combining acoustic meta-atoms and meta-molecules and simply rotating the scatterers. Both the simulated and experimental results demonstrate structure-dependent dual-band topological edge states. Such a design may provide new ideas for multi-channel acoustic communications and subwavelength acoustic energy harvesting.