Membrane-type acoustic metamaterial with eccentric masses for broadband sound isolation

Membrane-type acoustic metamaterials (MAM) are novel, lightweight and compact materials that can be used to isolate the sound at low frequencies beyond the limits of conventional materials. MAMs open up many possibilities for creating a new generation of acoustic materials and sensor devices. In this paper, the acoustic-structural interaction of the MAM with eccentric masses is explored by employing finite element simulations that use multi-physics commercial software COMSOL with experimental validation. This scheme is set to optimize the distribution of eccentric masses (such as thickness, weight, shape, the split number, the size of the ‘pocket’ and the size of the ring mass) to improve acoustic performance. The mass added onto the membrane can change the membrane surface density, constrain membrane displacement and induce new anti-resonance modes. Combinations of these new anti-resonances can broaden sound insulation performance of the MAM. The 4-split ring mass configuration can significantly increase the 5 dB-TL band by 1325% compared to that of a single membrane in the low-frequency range (<300 Hz). The gap between the splits, called a ‘pocket’, is examined to further explore the membrane-acoustic interactions in order to obtain a better understanding of the physical mechanism.