Effective density of air in open-cell polyurethane foam for ultrasonic frequencies

Abstract

This article deals with a theoretical analysis of the experimental results reported in a previous paper [K. Matsuzawa and M. Ochi, J. Acoust. Soc. Am. 68, 212–217 (1980)]. An approximate formula for the effective density of air in the foam is proposed as ρ = ρ0 [1+C(1+L)+M(1−j) δ1/(2R)], where ρ0 is the density of free air, C is the material concentration, j = (−1)1/2, δ1 is the viscous boundary layer thickness, R is the volume-to-area ratio of pores, and L and M are constants. Then, on the basis of the experimental data, it is found that L = 1.2 and M = 2.6 in common with the foam materials of various pore densities.