Acoustics of Porous Materials: Recent Advances Relating to Modelling, Characterization and New Materials

Recent advances in mathematical theory, numerical modelling and signal processing have enabled a number of sophisticated methods for the prediction and measurement of the acoustical properties of porous media to be developed. These results impact on the fields of general acoustics, noise and vibration control, polymer extrusion, pharmaceutics, medical research, soils and underwater sediment research. Although a considerable amount of related work has been carried out since 1940s, there are still a number of significant challenges associated with modelling of the acoustical behaviour of porous materials with heterogeneous structure, complicated shape and/or unconsolidated elastic frame. Other problems concern the efficiency, stability and convergence of numerical methods that are used to predict the efficiency of single porous layers and their composites. In addition, new classes of porous materials have recently emerged. These are auxetic foams, materials with double porosity, inclusions and anisotropic pore structure. The acoustical behaviour of these materials is yet to be fully understood and practically exploited. The aims of this special section of the journal are: (i) to present the most up-to-date developments in modelling, characterisation and applications of acoustic porous media, (ii) to communicate the advances in acoustics of porous media research to adjacent disciplines concerned with material technology, (iii) to discuss future challenges for this area of research. This section is a compilation of eight invited papers from well-known and emerging talented researchers working on acoustics of porous media. The first three papers in this section are mainly theoretical, the next three papers are largely numerical and the last two papers focus mainly on new materials and their applications. The first paper by German Maximov presents a new unified theory of sound propagation in porous media. The author uses the Hamilton’s and Onsager’s variational principles to derive a system of Biot-type equations that takes into account the fluid shear viscosity relaxation, thermal conductivity and expansion coefficients. This theory predicts the existence of two shear propagation modes Kirill Horoshenkov, University of Bradford, UK