Coupling and scaling effect for low-frequency broadband sound absorption via vertex-based hierarchy

On-demand noise remediation in the low-frequency broadband region remains a challenge. We present a hierarchical sound-absorbing meta-structure (HSM) to realize the desired low-frequency broadband absorptive performance at a subwavelength thickness. The physical mechanism underlying the superior performance is revealed through the coherent coupling effect and the hierarchical scaling effect that are both tied to the hierarchical characteristics. We experimentally validate the advocated absorptive merits of HSM and the predicting results. The quasi-perfect (α>0.9) bandwidth of the first-order HSM can be remarkably improved by 219% and 363% when it upgrades to the second- and third-order, respectively. This work may pave the way of designing acoustic meta-absorbers against low-frequency noise over a wide range.