Acoustic transmission characteristics based on coiled-up space metamaterials

Abstract

Coiled-up metamaterials with solid plate (SC) and with micro-perforated plate (MPC) are proposed for broadband low-frequency acoustic insulation and absorption. Firstly, the sound transmission theory of the double-layer plate and the impendence of the micro-perforated plate coupled with the coiled-up channel are introduced to obtain the dependence of structural parameters on the acoustic characteristics. Then, the acoustic performances of SC and MPC are investigated numerically and verified by experiments, and the effects of geometry parameters are analysed to predict the acoustic performance of SC and MPC. The minimum sound transmission loss (STL) of SC with a thickness of less than 2 cm is higher than 20 dB and the average STL reaches 45 dB at [0, 1600] Hz. The multi-order resonances of coiled-up space induce STL valleys but provide 10 dB improvement at valleys compared with double-layer plates. The MPC achieves narrow absorption at 422 Hz and 1232 Hz, which are induced by the resonances of coiled-up channels and 99.99 % of total energy dissipation is viscous dissipation mainly occurring in MPP. Coiled-up space with embedded porous materials (PTM) achieves above 0.9 absorption coefficient at [700, 1600] Hz. The optimized MPTMs, which consists of three parallel MPCs guided by the genetic algorithm (GA) and a single PTM unit, can reach a normal incident average absorption coefficient of 0.80 at [342–2000] Hz and a random incident absorption coefficient above 0.5 at [352–1862] Hz.