Porous Sound-Absorbing MaterialsPart II: Sound Absorption Mechanisms and Modeling

The first part of this paper discusses the importance of porous materials in passive noise reduction, types of porous materials, various applications of these materials, relevant acoustical and non-acoustical parameters, and different methods to measure them based on international standards were explained. In this part of the paper, definitions and experimental methods used in measuring the acoustic properties of the absorption coefficient and the sound transmission loss based on international standards are presented. Then, while providing a comprehensive discussion of the sound absorption mechanisms in porous materials, the types of sound absorption mechanisms, including viscous, thermal, and structural losses, are described. The effect of different parameters on the variation of sound absorption of porous materials has been presented. Also, various models, including experimental, laboratory, and analytical models used for expressing the acoustical and mechanical properties of porous materials, are discussed. Finally, a brief review is present for recent research areas on porous materials.