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Diffusion multiple par des cibles élastiques immergées.
Propagation d'ondes cohérentes et interactions résonantes.

Abstract : This work deals with the acoustic scattering by a random distribution of cylindrical shells in a fluid. This study
has three parts. The first one is about a limited number of shells. A resonant coupling is shown. This couple
induces a split of the A-wave (Scholte-Stoneley wave) resonances. These splits are experimentally validated.
The second part presents two effective media theories: Waterman and Truell's and the Fikioris and Waterman's
one. They consist in the analytic averaging of the scattered field with the positions of shells. The average wave
obtained is called the effective or coherent wave. The major difference between these theories is that Fikioris and
Waterman take into account the size of the shells whereas, in the Waterman and Truell theory, the radius of the
shells tends towards zero. These two theories allow the computation of an effective wave number. The influence
of the resonances of one shell is seen on the effective phase velocity and on the effective attenuation. The results
of these two theories are compared with the ones of a third theory: the one of Foldy. All these theories give
similar results for weak concentrations, but, for strong concentrations, the results of the theory of Fikioris and
Waterman differ from the others. The study of a slab-like region with randomly placed shells leads to the
determination of a reflection and a transmission coefficient. These are similar to the ones obtained by
considering a fluid slab. The analogy between the inhomogeneous medium and a viscous fluid is possible. The
experimental study of such a medium gives good results for the effective attenuation. The last part deals with
inhomogeneous media with the shells replaced by a set of two shells close enough to produce resonant coupling.
In this case, an effective wave number is obtained with the Fikioris and Waterman theory. The reflection and
transmission coefficients can be expressed as the ones of a fictitious fluid-like slab for which the phase velocity
and the attenuation would be dependent of the direction of propagation.
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Contributor : Pierre-Yves Le Bas <>
Submitted on : Thursday, July 20, 2006 - 4:26:24 PM
Last modification on : Tuesday, February 5, 2019 - 11:41:16 AM
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  • HAL Id : tel-00086985, version 1

Citation

Pierre-Yves Le Bas. Diffusion multiple par des cibles élastiques immergées.
Propagation d'ondes cohérentes et interactions résonantes.. Acoustique [physics.class-ph]. Université du Havre, 2004. Français. ⟨tel-00086985⟩

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