Bandwidth broadening for transmission loss of acoustic waves using coupled membrane-ring structure

Recently, membrane-type acoustic metamaterials have been found useful in eliminating low-frequency sound/noise. Those materials exhibit unusual vibroacosutic behavior and have a negative value in mass density. In this study, we present a new design of acoustic metamaterials that can effectively broaden sound attenuation zone and achieve acoustic negativity in mass density/bulk modulus. The proposed structure is comprised of two membranes and two ring masses which are attached on membrane surfaces, respectively. Both dipolar and monopolar resonance exist in the proposed coupled system, which makes acoustic negativity possible. By altering mass magnitude and membrane tension the transmission loss peak frequency can be easily tuned. With two membranes having two rings of different magnitudes, the attenuation bandwidth can be effectively broadened.