Subwavelength acoustic energy harvesting via topological interface states in 1D Helmholtz resonator arrays

We have theoretically and experimentally demonstrated subwavelength acoustic energy harvesting via topological interface states in 1D Helmholtz resonator arrays. The system can produce two types of bandgaps in the subwavelength realm due to the resonance and band folding mechanism, respectively. Through the analyses of the Zak phase and eigenfield distributions, the topological properties of band-folding-induced gaps can be changed by tuning the lattice structural parameters, while those of resonant gaps maintain stability. When two different arrays are spliced together, topological interface states will appear in the band-folding-induced band gaps but do not exist in the resonant gaps. The experimental measurements agree well with the theoretical prediction. Our study expands the applicability of acoustic topological insulators in a compacted platform.