Tunable Topological Edge Transport In Acoustic Meta-Atoms

Topological insulators (TIs) in condensed matter physics have been rapidly developed in acoustic fields and have enabled the controlling of acoustic waves in brand new ways recently. The current acoustic analogs of electronic TIs are mainly based on sonic crystal Bragg scattering. The practical applications of these TIs were restricted by a non-adjustable geometric structure, a wavelength equivalent scale, and a high and fixed frequency response. Here, we propose subwavelength acoustic TIs on the basis of negative metamaterials, which utilize local resonance different from Bragg scattering to design topologically protected acoustic propagation. We demonstrate the existence of band inversion by altering the ratio of the distance of the meta-atoms to the lattice constant. More importantly, the dispersion and edge states of the Dirac cones can offer tunability within a wide frequency range under a fixed lattice constant by adjusting the structural parameters of the meta-atoms. Theoretical analysis, numerical simulations, and experimental measurement verify the edge states of the acoustic TIs. The proposed acoustic topological metamaterials provide a flexible way of manipulating sound propagation.