Effect of the three-dimensional microstructure on the normal incidence sound absorption coefficient of foams: A parametric study

Fabien Chevillotte (1) , Camille Perrot (2)

1 Matelys
2 MSME - Laboratoire de Modélisation et Simulation Multi Echelle

Sound absorption arises mainly from visco-thermal dissipation of a pressure wave propagating through a porous material. First-principal calculations and X-ray computed tomography experiments reveal that the sound absorbing behavior of real foam samples made from dispersion of gas bubbles in liquid matrices can be directly described from a simple three-dimensional regular model of hollow spheres, which opens new avenues for optimal design of acoustic materials. However, the proper choice of bubble and interconnection sizes, two critical parameters of the foam's morphology, depend on the sample thickness, the frequency range of interest (the choice of the optimization criterion), and the kind of excitation (normal or diffuse incidence). This presents a problem: a small interconnection combined with large pores is necessary for thin sample thicknesses in order to provide a resistive and tortuous layer of porous sample, but interconnections have to be larger and pores smaller for thicker samples to be able to dissipate viscous energy in all the thickness of the material by avoiding an excess of reflected waves. Moreover, the manufacturing process places constraints on the accessible range of porosities and pore radius. The selected criterion is a sound absorption average over third octave bands between 125 Hz and 4000 Hz. In this communication, massive computations are therefore used to provide guidelines for selecting the appropriate foam's morphology. This study is restricted to normal incidence.

Domains: Acoustics [physics.class-ph]

Fabien Chevillotte, Camille Perrot. Effect of the three-dimensional microstructure on the normal incidence sound absorption coefficient of foams: A parametric study. 22nd International Congress on Acoustics (ICA 2016), Sep 2016, Buenos Aires, Argentina. ⟨hal-01664290⟩