Theories for sound propagation in rigid‐framed porous materials

Abstract

An historical overview of the development of theories for sound propagation in rigid‐framed porous media is offered. Phenomenological and microstructural theories are contrasted. Microstructural approaches may start either from specifications of the geometrical form of the solid frame or from specifications of the geometrical form of the pores. The former approach is particularly useful for describing acoustical properties of fibrous materials. The latter approach has the longest history, the wider application, and is the basis of many recent developments in the dynamic theory of poroelasticity. In one form of the pore‐based theory, consideration is given to the incorporation of dynamic effects of pore shape and irregularity and steady flow tortuosity. An alternative form results from a more rigorous approach to the effects on viscous drag and thermal interaction with pore walls of the inclination of pore axes to the macroscopic pressure gradient, i.e,, dynamic tortuosity effects. By comparing theoretical predictions with experimental data for sand, lead shot, glass heads, and snow, both the usefulness and the current limitations of theories that use microscopic pore‐based descriptions and their various approximations are explored.