Résumé
In order to analyze coupled resonances, the formalism of the transition matrix is used. We measure at normal incidence R and T, the reflection and transmission coefficients of two aluminum plates separated by a very thin water layer. The transition terms are linear combinations of R and T and the coupled resonances appear in separate terms. Under the condition that the previous coefficients have been recorded with a common phase reference, it is possible to isolate the resonances well. The vertical mode and the resonances of the water layer can be easily located on the spectra of the experimental transition terms. The shifts between the resonances of the structure and the resonance frequencies of the symmetric and antisymmetric modes of a unique plate are exhibited as well. The transition terms are very efficient tools for characterizing coupled systems.