A study on the energy and the reflection angle of the sound reflected by a porous material

Many noise control applications are based on the use of porous materials; therefore, it is important to have a tool to simulate acoustic behaviours. Plane-wave acoustic properties such as the sound absorption or reflection coefficient at normal incidence can be quickly obtained using standing wave tube or theoretical models and can be used to select the type of porous material and its dimensions. However, in real situations, no plane wave exists, and the sound field is more complex. Therefore, it is interesting to understand the real behaviour of porous materials. In this paper, a simple case of a point source above a uniform infinite layer of porous material has been analysed. Conversely, to the case of a plane wave excitation, on the porous material surface different incidence angles can be observed and the phase relation between the pressure and the particles velocity should be considered. The aim of this work is to define the far and the near field above a porous material where the results obtained considering a plane excitation may or may not be respectively extended. For this purpose, two parameters have been introduced: the energetic deviations index and the true reflection angle.