Ultrabroadband sound absorption enabled by a hybridized soft boundary
Phys. Rev. Applied 25, 014036 – Published 14 January, 2026
DOI: https://doi.org/10.1103/228r-tgj1
Abstract
Acoustic metamaterials open compelling avenues for ultrathin low-frequency sound absorbers, yet their reliance on localized resonances renders a fundamental trade-off between deep-subwavelength thickness and attainable bandwidth. Therefore, achieving broadband absorption necessitates the spectral overlap of numerous resonant modes, inevitably resulting in intricate architectures that impede their practical applications. Moreover, sound absorbers under a rigid backing, constrained by the acoustic analogue of the Rozanov bound, remain inherently bulky when operating at extremely low frequencies. In this study, we put forward a paradigm to implement an ultrabroadband acoustically soft boundary via hybridizing an opening boundary with underdamped resonators. By coupling a thin layer of porous material to this hybridized soft boundary, we demonstrate an ultrabroadband absorber that achieves an average absorption of 92.5% in simulations and 91.4% in experiments across the 20- to 3000-Hz frequency range. The demonstrated absorber features an ultracompact profile, measuring a thickness of just 2.8 cm, and a simple configuration, consisting of only three resonant meta-atoms. We further apply the proposed absorber as an anechoic termination or a perfectly matched layer within a standard test system for measuring acoustic scattering coefficients, offering a more efficient and compact alternative than traditional apparatus composed of a 30-cm-thick sponge. This work offers a promising pathway toward compact ultrabroadband sound absorbers for practical applications.
