ASTRIDE LOCALIZATION IN CAVITIES FILLED WITH AN IRREGULAR ABSORBER

The properties of wave oscillations in confined systems constitutes a classical subject of physics with applications in acoustics, electromagnetism, and quantum systems. Simple to study in the case of clas-sical geometries, they exhibit non trivial localization effects as soon as the confined geometry exhibit some kind of irregular behavior. In the case of acoustic cavities, these localization effects give rise to a specific enhancement of the damping as they confine some of the eigenmodes on the irregular frontier where the dissipation mainly occurs. These results, obtained for any irregular resonator, whatever the shape and characteristic sizes of its boundary, have been shown in the case of surface absorption but the question is raised of the impact of geometrical irregularity when the dissipation occurs in the bulk of a material instead of its surface. Cavities partially filled with a smooth absorbing material present eigenmodes that are essentially localized either in the non-absorbing volume or in the absorbent. It is shown here that for irregular shaped absorbent material there appears a new type of localization, “astride ” localization, for modes which exist in both regions. It is these modes that are specifically efficient in dissipating the energy