A broadband acoustic panel based on double-layer membrane-type metamaterials

Low-frequency noise is a growing problem in large structures of modern transportation technologies. In this study, we report a large-scale acoustic panel made of double-layer membrane-type metamaterials (DMAMs) for broadband noise reduction. A complete theoretical model based on the unit cell is fully developed and extended for finite multi-celled membrane-type acoustic metamaterial (MAMs) array. A large-scale acoustic panel constructed from 8 × 8 DMAM unit cells is proposed. To deal with the global compliance of the large-scale support structure, the double-layer panel frame structure with large bending stiffness is designed to shift the global resonances to higher frequencies and provide an efficient way to well maintain the MAM's performance. Moreover, the double-layer configuration further guarantees ultra high transmission loss within the frequency range of interest. Experiments are carried out to validate the analytical and numerical predictions. Excellent transmission loss ranging from 20 to 59 dB within ten third octave bands (0.32–2.5 kHz) is observed, deeply breaking the mass density law. We believe the proposed design and the associated theoretical model could serve as an efficient tool for designing acoustic metamaterial-based panels and soundproof walls with high noise reduction in low/middle frequency regions.