An approach to broaden the low-frequency bandwidth of sound insulation by regulating dynamic effective parameters of acoustic metamaterials

In this paper, an approach is proposed to broaden the low-frequency bandwidth of sound insulation by regulating dynamic effective parameters of acoustic metamaterials (MAMs). First, a flexible membrane-type acoustic MAM sample consisting of a homogenous polyimide membrane and a perforated ethylene vinyl acetate copolymer (EVA) plate is designed, in which the membrane within each hole is represented as a local resonator without any additional mass. Next, the formation mechanisms of the trough, peak and bandwidth of sound transmission loss (STL) are profoundly expounded through the analyses of average normal displacement (d(_z)), coupling vibration characteristics and zero-boundary effective parameters. All of this has shown that the lower limit, peak frequency and upper limit of the STL bandwidth can be regulated by the vibration modes of the lumped coupling resonance, anti-resonance and local resonance, respectively. In addition, the structural and material parameters of the MAM unit are quantitatively analyzed, simultaneously, the regulation approaches of the zero-boundary effective parameters and the transfer characteristics of the STL bandwidth are also demonstrated. Finally, we have proposed two improved lightweight proposals based on the broadening mechanisms of the STL bandwidth. The results show that the STL bandwidth can be greatly broadened between 80 Hz and 800 Hz, and the STL on average is 12.2 dB higher than that of a homogenous EVA plate. The MAM samples not only provide a sufficient strength and a long lifecycle, but also help to eliminate the dependence of the membrane tension.