Quasi-perfect absorption by sub-wavelength acoustic panels in transmission using accumulation of resonances due to slow sound

TL;DR

This paper demonstrates how sub-wavelength acoustic panels with Helmholtz resonators can achieve near-perfect sound absorption at low frequencies by leveraging slow sound phenomena and resonance accumulation.

Contribution

It introduces a novel design of resonant panels that utilize slow sound and resonance accumulation for enhanced low-frequency sound absorption including transmission.

Findings

Achieved quasi-perfect absorption in sub-wavelength panels.

Demonstrated the role of slow sound in shifting cavity resonances.

Validated the design through theoretical and experimental methods.

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.