Boundary-dependent corner states in topological acoustic resonator array

Higher-order topological insulators (HOTIs) capable of hosting multi-dimensional topological states have been considered as a significant platform for wave regulation. Here, based on a “breathing” kagome lattice composed of coupled tube resonators, we demonstrate the topological phase transition induced by tuning the nearest-neighbor interactions of the tubes. Crucially, beyond the nontrivial bulk polarization, we unveil that the behaviors of the higher-order topological states are also affected by the boundary conditions, which enriches the design of the desired HOTIs. Along these lines, we propose two prototypes of acoustic topological devices and experimentally exhibit two promising applications of the topological corner states for frequency-selected energy harvesting in different conditions. Our work extends the applications of the higher-order topological states in resonant acoustic systems and provides diverse routes for designing topological devices on a subwavelength scale.