Double-panel metastructure lined with porous material for broadband low-frequency sound insulation

Insulating low-frequency sound using lightweight structures is very difficult according to the classical mass law. To challenge this problem, we present a comprehensive theoretical analysis and experimental verification of the sound transmission loss (STL) of double-panel metastructures (DPMSs) composed of two layers of metamaterial plates lined with a porous material (PM) layer. To facilitate the analysis, an efficient semi-analytical approach based on the transfer matrix method is proposed to predict the normal, oblique and diffuse field STL of the DPMS with PM. The effects of various structural and material parameters on the STL of the DPMS are analyzed. Some parameters that have significant influences are revealed. Based on semi-analytical predictions and experimental measurements, we demonstrate that an appropriately designed large-scale DPMS lined with PM can achieve a diffuse field STL being much higher than the mass law over a broadband low-frequency range below 500 Hz. More interestingly, compared with the conventional double layer homogeneous plates lined with PM (with the same total mass and thickness), the DPMS lined with PM also has a significantly improved diffuse field STL at broadband low frequencies below 500 Hz.