Subwavelength higher-order topological insulator based on stereo acoustic networks

摘要

Recently, the concept of a higher-order topological insulator has prompted increasing scientific interest in achieving the lower-dimensional boundary states. Among them, the zero-dimensional topological corner states in 2D/3D stereo acoustic systems are sustained in the second-/third-order topological insulators. However, the wavelength-scale unit size limits the application potential of corner states in acoustics, and the acoustic third-order topological insulator with a subwavelength unit cell is in urgent need to be proposed. Here, we use sub-wavelength acoustic waveguide networks to construct sonic lattices and configure the waveguide size to modulate the coupling strength in both 2D and 3D systems. The topological corner mode of second-/third-order topological insulators appears when the intra-cell coupling strength is weaker than the inter-cell one. Through calculating the eigenfrequencies and simulating the intensity response, the existence of a topological 2D surface, 1D hinge, and OD corner states is ascertained. We demonstrate that the proposed topological acoustic corner mode may have potential applications in realizing the sound confinement and energy harvesting in both 2D and 3D systems.