Investigation into the sound insulation performance of layered membrane-type acoustic metamaterials enhanced by damping

Abstract

Traditional membrane-type acoustic metamaterials have a narrow sound insulation bandwidth (typically a few hundred Hz) and a low sound transmission loss (STL) dip (mostly below 5 dB) at low frequencies. Researchers have attempted to widen the bandwidth by altering the mass block structure and designing layered membrane-type acoustic metamaterials (LMAM). However, the first STL dip has not been improved. A LMAM consisting of double-layer membranes lined with Polyvinyl Chloride (PVC) gel has been proposed in this study. The low stiffness and high damping of PVC gel enhance sound energy absorption, improving the STL dip and broadening the effective sound insulation range at the same time. Impedance tube experiments have been conducted to study the effect of the PVC gel thickness and presence/absence of the air interlayer. Then the experimental results have been reproduced by numerical simulation to explore the sound insulation mechanism in detail at STL dip and peak frequency. The deformation of LMAM is connected to the sound insulation coefficients to explain the variation of the STL curve. The proposed LMAM, with a thickness of less than 20 mm, enhances the STL dip by approximately 17 dB and meanwhile maintains excellent performance at the STL peak. It avoids the rapid reduction in the middle-high frequency and breaks the mass law over an ultra-wide frequency range (420–2520 Hz). The wide availability of high damping materials endows this design strategy with robust vitality, which can show great potential for noise control engineering.