Broadband low-frequency membrane-type acoustic metamaterials with multi-state anti-resonances

In this paper, a well-designed low-frequency membrane-type acoustic metamaterial (MAM) with continuous multi-state anti-resonance modes is proposed, which may effectively broaden a sound attenuation zone in low-frequency regime and produce single-negative effective parameter characteristic. Firstly, four lightweight MAM samples with distinct resonator distributions are purposefully designed, based on the low-order vibration characteristics of membrane and the design concept of dynamic balance. Then, the realization principle of the multi-state anti-resonance modes and the regulation mechanism of the sound transmission loss (STL) are progressively compared and investigated. Among them, a cross-like resonator easy to achieve dynamic balance is capable of offsetting and broadening the STL bandwidth, and eliminates node-circle-type oscillation mode. Additionally, a MAM sample whose sub-resonators are improved in distributions is proposed, wherein the structure and material parameters of the sub-resonators are symmetrical and interlaced. This sample shows 15 hybrid low-order anti resonance modes within the STL bandwidth, and achieves an excellent ability to insulate the broadband noise between 48 Hz and 736 Hz. Furthermore, its STL performance could be proved, between 72 Hz and 560 Hz, by a homogeneous ethylene vinyl acetate copolymer plate. Secondly, the coupling characteristics between this sample and the sound field are revealed in detail, through the analyses of effective parameters, surface-averaged normal displacement, coupled kinetic energy and the coupled vibration behaviors. Finally, the low-frequency STL performance of a large-scale MAM plate sample with one supercell as a periodic unit is verified by simulation and experiment. This paper proposes a lightweight, flexible and ultrathin distributed MAM structure that can produce continuous multi-state anti-resonance modes, which may promote the engineering application investigations of the broadband low-frequency MAMs to some extent. (C) 2019 Elsevier Ltd. All rights reserved.