N-shell cluster in water: Multiple scattering and splitting of resonances.

Clusters of N thin parallel and identical shells (aligned or not! in water are considered. Assuming a harmonic plane wave is normally incident upon one cluster, the scattered-field classical expression is recalled, and then computed for different types of clusters, along with resonance spectra. The scattering S matrix is defined, and its unitarity property used to check the numerical results. All spectra are compared with that of a single shell, in the frequency range where resonances are due to an A-wave phase matching only. Whatever the cluster, each resonance of the single shell is seen to split into M different ones. The value of M depends on the number of shells, the distance between them, and the symmetries of the cluster. Apart from the very special case of aligned shells (M 52N), no simple law has been found to predict the value of M. [ABSTRACT FROM AUTHOR]