Controllable subwavelength topological rainbow trapping in water-filling acoustic metamaterials

Due to the great application potential in programmable wave transportation, topological metamaterials have gained enormous research attention in recent decades. This article proposes an acoustic metamaterial that is composed of a perforated nylon substrate and a ceiled air-flowing channel. The holes arranged in a honeycomb lattice are filled with water to tune the resonance frequency and topological phases. Two subwavelength bandgaps are opened by tuning the height of water columns, and controllable bandgap and topological phase transitions are subsequently obtained. Generally, the chirality conflict between different unitcells is designed to generate topological protected interface modes where energy is localized within close vicinity of the interface. After studying on the dependence of topological protected interface mode frequency and quality factor on water height, a design strategy is proposed to obtain high-quality topological protected interface mode at the target frequency. Two waveguiding paths are designed to study the wave propagation behavior along the interface under different excitation frequencies. Topological rainbow trapping which can terminate waves at different frequencies and different locations is finally demonstrated. The controllable bandgap and TPIM allow the topological structural designs to avoid complex structures and high cost. © 2023 Elsevier Ltd. All rights reserved.