Improvement of sound absorption and insulation using a double-layer metamaterial (DM) in the acoustic free field is proposed in the present paper. The front layer of the DM is composed of a flexible micro-perforated plate with periodic local resonators, the backing layer is a flexible plate attached with periodic local resonators too, and an air gap exists between the double plates. Good agreement is gained between the results of the theoretical prediction and finite element simulation for the DM and the original double-layer plate (DP) while considering the vibroacoustic coupling between the sound excitation and the plates. Both theoretical and simulation results verify that the local resonators can improve the sound absorption and insulation of the DP. The underlying mechanism of the DM is investigated using the acoustic impedance and displacement pattern. Filling the gap with the porous material can further improve the sound absorption and insulation of the DM. Finally, the influences of the number and additional mass ratio of local resonators on the acoustic performance of the DM are investigated, and the practical realization of the DM is verified. The present design shows great potential for practical noise reduction in the free field.

中文翻译：

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使用双层超材料改善吸声和隔音效果

本文提出了使用双层超材料（DM）在自由声场中改善吸声和隔音效果。DM的前层由具有周期性局部谐振器的柔性微孔板组成，背衬层也是具有周期性局部谐振器的柔性板，并且在双板之间存在气隙。在考虑到声激励和板之间的振动耦合的同时，DM和原始双层板（DP）的理论预测结果和有限元模拟结果之间取得了很好的一致性。理论和仿真结果均证明，本地谐振器可以改善DP的吸声和隔音性能。使用声阻抗和位移模式研究了DM的基本机制。用多孔材料填充间隙可以进一步改善DM的吸声和隔音效果。最后，研究了局部谐振器的数量和附加质量比对DM声学性能的影响，并验证了DM的实际实现。本设计显示出在自由场中实际降低噪声的巨大潜力。