Broadband low frequency noise attenuation using thin acoustic metamaterials for aircraft cabin noise mitigation

Broadband noise attenuation at low frequencies is a challenge for the aeronautical, ground transportation and construction industries. In the past few decades, various low frequency noise control solutions, based on acoustic metamaterials designs, have been presented in the literature. The proposed technologies showed promising acoustic performance and are considered as better solutions when compared to conventional sound insulation materials in application fields such as aerospace, where the available space for their integration is extremely limited. The noise attenuation of typical metamaterials is characterized by very narrow resonant frequency maxima which represent a good solution for tonal noise. However, in practical applications, the slight variations of the tonal noise frequencies may render a metamaterial ineffective. This paper presents a thin acoustic metamaterial design for improved broadband noise attenuation at low frequencies. 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. A thermo-viscous acoustics approach was solved numerically with COMSOL Multiphysics in the frequency domain to predict the sound absorption coefficient and the normal incidence sound transmission loss of the proposed metamaterial design. The results obtained show a wide frequency band noise attenuation for this metamaterial at low frequencies.