On the use of porous inclusions to improve the acoustical response of porous materials: Analytical model and experimental verification

Acoustical composite materials obtained through a set of porous inclusions are studied. A theoretical model based on the homogenization hypotheses introduced by Boutin et al. is presented; the inclusions are supposed periodic and the frame rigid. The idea behind the inclusion of a second acoustical porous material into the original single porosity material, is to obtain the pressure diffusion effect already observed in the double porosity case. At the same time, the main disadvantages of double porosity are faced, especially the absorption behavior at very low frequency and the loss of performances in transmission. Experimental data are obtained in Kundt Tubes of different dimensions in terms of absorption curves and compared to analytical results for representative configurations, thus validating the theoretical model.