Reconfigurable topological transition in acoustic metamaterials

Acoustic topological insulators inspired by quantum Hall effects exhibit topologically protected edge states and offer great potential for manipulating sound waves. However, most two-dimensional acoustic topological insulator systems are severely hindered by fixed geometry and frequency responses, structure scale comparable with the wavelength, and a single topological phase-transition mechanism. Few studies have investigated edge states with dispersion tunable, reconfigurable lattice, and subwavelength-scale control over sound topological states. Here, a subwavelength-scale and tunable topological metamaterial based on local resonance is realized by constructing a honeycomb lattice with open-hole hollow tube. The topological metamaterial is radically distinct from sonic crystal topological insulators based on Bragg scattering. The corresponding band structure of the proposed honeycomb cell possesses double-degenerate Dirac cones. We introduce the symmetry-breaking mechanism to establish reconfigurable topological insulators by simply rotating the side hole of the metamolecules or shrinking and expanding the metamolecule spacing to mimic the pseudospin states with opposite Chern numbers and realize topological phase transition. Results provide a basis for exploring subwavelength-scale control sound propagation and analyzing topological phase-transition mechanism.