### ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

## 5aPAa1. A numerical approach of the transmission of a polyurethane foam
sphere in an impulse regime.

**Abdelkader Sfaoui
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*Laboratoire d'Acoustique, U.F.R. de Physique, P5, Villeneuve d'Ascq 59655,
France
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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.