Experimental Realization of Three Types of Acoustic Localized States at Topological Interface

Wave localization has been the subject of extensive investigation due to its crucial importance in both applied and fundamental research. In particular, the focus has shifted to topologically protected states and flatband states. Here, we develop an acoustic topological heterostructure with one dispersive band and one flatband. In the bandgap, there is one topological state and two defect states. Drawing on this topological heterostructure, we combine three different types of wave localization and realize the flatband bound states, topological interface state, and defect states in both theory and experiment. Then, we examine how the localization of these three types of localized states varies with respect to the local coupling coefficient κBI. Our findings indicate that the topological interface state is robust in relationship to local parameter κBI, while two defect states are strongly influenced by this parameter. As for the flatband states, their eigenfrequencies are unaffected by parameter κBI, but the flatband bound state around the topological interface is dependent on this parameter. Additionally, by modifying the excitation conditions, three types of localized states can be transformed into each other. Leveraging the advantages of the localization of different types of localized states, our proposal represents a significant advancement in the potential applications of acoustic sensors and filters.