A systematic link between microstructure and acoustic properties of foams: A detailed study on the effect of membranes

Abstract : In this study, we show how milli-fluidic tools can be used to elaborate polymer foams with tunable microstructural parameters, such as the size and the connectivity of the pores. We produce several samples having the same density and the same monodisperse pore size but different values of the closure rate of the windows separating the foam pores, which is estimated by measuring the proportion of closed cells and the size distribution of apertures for open-wall cells. This distribution is based on a distinction between the windows counting four or less edges from the windows counting more than four edges. Then a representative unit cell is reconstructed to mimic the main feature of microstructure information and serves as the basis to the computation of the sound absorbing parameter, using numerical homogenization techniques. Very good correspondences between numerical results and experimental measurements were observed. Our analysis reveals a significant dependence of membrane level on the sound absorption behavior of these foams.