## Characterization of porous acoustic materials. State of the art.

Walter Lauriks,

KU-Leuven, Belgia.

More than 60 years ago, Zwikker and Kosten published their book ‘Sound Absorbing Materials’[1]. In this book, they present models to predict the behaviour of acoustic materials, based on their microstructure. The work of Zwikker and Kosten can be considered as an extension of earlier work of Rayleigh and Kirchhoff. The strong point of this book is that apart from theoretical models, experimental devices are described to measure the input parameters of the models. Since then, a lot of work has been done by Biot [2], Attenborough [3], Allard [4] and others and the models have been optimised to take more physical effects into account and to provide a physical unambiguous definition of the material parameters. Parallel to the improvement of the models, experimental techniques were designed to measure the material parameters independently. In this paper, we give an overview of the experimental techniques that have been developed over the last fifteen years.