Regulation of acoustic topological state in two-dimensional Su-Schrieffer-Heeger model based on airflow circulation

In this work, we propose a method for regulating topological states in acoustic systems by introducing airflow circulation. Composed of hollow rings linked with subwavelength rectangular waveguides, the proposed acoustic topological meta-crystals support multi-dimensional boundary states where the corner states merge into the edge ones. With the airflow introduced, the corner states separate from the edge states. We give the relationship between the frequency of the corner state and the speed of airflow and test the result by calculating eigenmodes of the supercell and finite lattice. Simulations for the acoustic field excited by a point source in a finite lattice also agree the relationship we give. The introduction of airflow in a topological system provides a method for manual control of the topological corner states.