A novel membrane-type acoustic metamaterial with a high sound transmission loss\n(STL) at low frequencies (500Hz) was designed and the mechanisms were investigated\nby using negative mass density theory. This metamaterial�s structure is like a\nsandwich with a thin (thickness=0.25mm) lightweight flexible rubber material within\ntwo layers of honeycomb cell plates. Negative mass density was demonstrated at\nfrequencies below the first natural frequency, which results in the excellent lowfrequency\nsound insulation. The effects of different structural parameters of the membrane\non the sound-proofed performance at low frequencies were investigated by\nusing finite element method (FEM). The numerical results show that, the STL can be\nmodulated to higher value by changing the structural parameters, such as the membrane\nsurface density, the unite cell film shape, and the membrane tension. The acoustic\nmetamaterial proposed in this study could provide a potential application in the\nlow-frequency noise insulation. C 2016 Author(s). All article content, except where\notherwise noted, is licensed under a Creative Commons Attribution (CC BY) license\n(http://creativecommons.org/licenses/by/4.0/). [http://dx.doi.org/10.1063/1.4942513]
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