Laboratoire d'Acoustique, U.F.R. de Physique, P5, Villeneuve d'Ascq 59655, France
Among the phenomena envolved in the propagation of an acoustic wave in a diphasic medium such as a polyurethane foam, there is the air/structure interaction. According to the Biot theory the latter is characterized by two parameters: (rho)[inf a] the inertial coupling and b the resistivity of the fluid flow. When the material porosity, the Young's modulus, and the Poisson's ratio are determined [G. Deprez, J. Phys. Suppl. C2, 43--52 (1990) and A. Sfaoui, J. Acoust. Soc. Am. 97, 1046--1052 (1995)], it is sufficient to adjust these parameters to describe the acoustic propagation. In this aim, an experimental technique has been elaborated. It consists in studying the transmission of a broadband impulse by a foam sphere. The transmission coefficient is obtained after time filtering and fast Fourier transform calculation of two signals: the incident signal and the transmitted signal at the center of the sphere. By selecting the curve to fit the Young's modulus data [A. Sfaoui, J. Acoust. Soc. Am. 97, 1046--1052 (1995)] by means of a regression program, the transmission coefficient is numerically analyzed in the range of 0--20 kHz. It follows that the transmitted signal is the superimposition of the Biot fast and slow waves.