This work deals with the acoustic scattering by a random distribution of cylindrical shells in a fluid. This studyhas three parts. The first one is about a limited number of shells. A resonant coupling is shown. This coupleinduces 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'sone. They consist in the analytic averaging of the scattered field with the positions of shells. The average waveobtained is called the effective or coherent wave. The major difference between these theories is that Fikioris andWaterman take into account the size of the shells whereas, in the Waterman and Truell theory, the radius of theshells tends towards zero. These two theories allow the computation of an effective wave number. The influenceof the resonances of one shell is seen on the effective phase velocity and on the effective attenuation. The resultsof these two theories are compared with the ones of a third theory: the one of Foldy. All these theories givesimilar results for weak concentrations, but, for strong concentrations, the results of the theory of Fikioris andWaterman differ from the others. The study of a slab-like region with randomly placed shells leads to thedetermination of a reflection and a transmission coefficient. These are similar to the ones obtained byconsidering a fluid slab. The analogy between the inhomogeneous medium and a viscous fluid is possible. Theexperimental study of such a medium gives good results for the effective attenuation. The last part deals withinhomogeneous 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 andtransmission coefficients can be expressed as the ones of a fictitious fluid-like slab for which the phase velocityand the attenuation would be dependent of the direction of propagation.
