Quasiperfect absorption by subwavelength acoustic panels in transmission using accumulation of resonances due to slow sound

TLDR

In the slow‑sound regime, cavity modes in the slits are down‑shifted, making the slit behave as a sub‑wavelength resonator. The study reports sub‑wavelength panels that achieve low‑frequency quasi‑perfect sound absorption, including transmission, by accumulating cavity resonances through slow sound. The panels consist of periodic horizontal slits loaded with identical Helmholtz resonators, producing strong dispersion, near‑zero phase velocity, and an accumulation of cavity resonances at the band‑gap edge. At the accumulation frequency, simultaneous symmetric and antisymmetric quasi‑critical coupling is achieved, enabling quasi‑perfect absorption with transmission using only monopolar resonators.

Abstract

We theoretically and experimentally report sub-wavelength resonant panels for low-frequency quasi-perfect sound absorption including transmission by using the accumulation of cavity resonances due to the slow sound phenomenon. The sub-wavelength panel is composed of periodic horizontal slits loaded by identical Helmholtz resonators (HRs). Due to the presence of the HRs, the propagation inside each slit is strongly dispersive, with near-zero phase velocity close to the resonance of the HRs. In this slow sound regime, the frequencies of the cavity modes inside the slit are down-shifted and the slit behaves as a subwavelength resonator. Moreover, due to strong dispersion, the cavity resonances accumulate at the limit of the bandgap below the resonance frequency of the HRs. Near this accumulation frequency, simultaneously symmetric and antisymmetric quasi-critical coupling can be achieved. In this way, using only monopolar resonators quasi-perfect absorption can be obtained in a material including transmission.