Method for Characterizing the Acoustic Properties of Thin Metamaterials Capable of Attenuating Broadband Noise at Low Frequencies.

Abstract

Controlling broadband noise at low frequencies is a challenge for the aerospace, ground transportation and construction industries. In the few past decades, various low-frequency noise control solutions based on acoustic metamaterial designs have been presented in the literature. The proposed solutions have shown promising acoustic performance and are considered better solutions compared to conventional sound insulation materials. However, the resonance frequencies of these metamaterials are narrow. Our recent work has shown that a parallel assembly of two structured materials allows the broadening of the first resonance frequency at low frequencies. The finite element method was used to characterize the acoustic attenuation performance of the metamaterial. This method requires a large computation time and is not suitable for a metamaterial optimization problem. This article presents an approach based on the transfer matrix method in series and in parallel to quickly and accurately predict the acoustic properties of the metamaterial. The geometry is an assembly of structured materials arranged in parallel and embedded in a layer of fiberglass. The two structured materials are designed such that their resonant frequencies are optimally regrouped to create a resonant frequency band of maximum attenuation at low frequencies. The sound absorption coefficient and the sound transmission loss at normal incidence predicted with the present approach are in good agreement with those obtained using the finite element method. In addition, the results obtained show a wide frequency band noise attenuation for this metamaterial at low frequencies.