Multilayer coupled plate-type acoustic metamaterials for low-frequency broadband sound insulation

Acoustic metamaterials have been becoming a popular topic for the better sound insulation at low frequency than traditional materials. However, due to the local resonance mechanism, this excellent performance can only be demonstrated in narrow frequency bands. Therefore, multilayer coupled plate-type acoustic metamaterials (MPAM) are proposed in this paper. The structure consists of a large plate-type acoustic metamaterial (PAM) with periodic square metamaterial units and double-layer fibers with different densities. According to finite element study on the insertion loss (IL) of the MPAM, the governing physical mechanism of the MPAM was analyzed according to the sound pressure level distributions and the vibration modes of the PAM layer. In addition, large-scale MPAM samples with a size of 506 mm*506 mm were manufactured, the reverberation and anechoic chamber was employed to verify the sound insulation performance. It can be concluded from the test results that the IL peak originate from the anti-resonance of the PAM layer rather than the weight of the materials. Compared to the structures without PAM layer, in the range of 360 Hz−950 Hz, the IL is increased by 5 dB at least and up to 17 dB at most. The influences of the incident angles, the frame density and the coverage rate of the PAM layer on the IL are disscussed. The proposed MPAM structure, analytical techniques and test results may be helpful for the engineering application of acoustic metamaterials.