Acoustic wave absorption and mitigation by porous metamaterial structures

Efficient noise control is an important and crucial issue in a wide range of engineering applications. Porous materials with dispersed micro-pores are commonly used due to their high capacity to absorb acoustic wave energy and mitigate undesirable noises. This thesis aims to improve the low-frequency sound absorption performance in a broad frequency range. For this purpose, two porous metamaterial (PM) structures are proposed, namely, the slit-perforated multi-layered porous metamaterial (SMPM) structure and the novel multiscale porous metamaterial (MPM) structure. The SMPM structure consists of periodic porous matrix layers and second-type porous layers with periodically distributed slits, while the novel MPM structure consists of a porous matrix with periodically distributed meso-pores, in which a second porous layer is introduced as an interlayer between the matrix and the meso-pores. Theoretical models based on the homogenization schemes and semi-phenomenological approaches to describe the macroscopic dynamic properties of the porous materials are adopted, while numerical methods based on the transfer matrix method (TMM) and the finite element method (FEM) are applied to compute the acoustic wave absorption and mitigation characteristics of the proposed PM structures in both room-temperature and high-temperature environments. In particular, the band structures or dispersion curves especially the frequency bandgaps, and the acoustic wave absorption coefficients are analyzed and discussed in details.
The research findings and the knowledge gained in this thesis may provide a deep insight into the acoustic wave absorption and mitigation characteristics and the corresponding physical mechanisms in porous metamaterial structures, which are highly valuable for the design, optimization, realization and application of novel porous metamaterial structures