Low-frequency acoustic edge modes based on a triangular maze

Abstract

For several years, acoustic topological insulators have received attention due to their unique ability to manipulate acoustic waves. However, acoustic wave manipulation due to acoustic topological insulators is based on Bragg scattering. This results in the wavelength being bounded by the lattice constant. In this paper, a new ultra-low frequency acoustic topological insulator structure is proposed using the labyrinth model in acoustic metamaterials. With a lattice constant of a0 = 60 mm, the unidirectional transmission frequency possessing a topologically protected edge state can be reduced to 684 Hz. This frequency is much lower than that of other structures with equal lattice constants. The length of the resonant cavity can be greatly increased by utilizing a triangular labyrinth structure at the symmetric position. Subwavelength Dirac cones can be constructed in the energy band structure by utilizing the local resonance effect. Topological phase transitions characterized by opposite valley Chern numbers can be achieved by changing the rotation angle of the scatterer. The results of simulations and numerical calculations verify the existence of a topology-protected unidirectional transmission edge state on topological boundaries. The properties of this edge state remains extremely robust in the presence of defects such as misordering, cavities, and corners. The research in this paper provides a efficient structure for controlling low-frequency acoustic waves.

Low-frequency broadband valley transport for acoustic topology based on extended resonance

“…Some researchers have also proposed the concept of topological acoustic polarisers, using the unique properties of resonant metamaterials as a platform for inducing topological nontrivial states. They extend the application field of topological acoustics to the low-frequency range [29,[36][37][38]. By this method it is possible to reduce the operating band to the low frequency range of 485 Hz, but with a bandgap width of only 5 Hz [37].…”

“…In addition, some researchers have proposed a triangular labyrinth structure. Based on ensuring the lattice symmetry, the length of the resonance cavity is greatly increased by folding the cavity, thus reducing the operating band to 685 Hz [38]. The width and length of the folded resonance cavity are limited due to the limitation of the size of the scatterer.…”