Localization and increased damping in irregular acoustic cavities

The present study is concerned with the properties of 2D shallow cavities having an irregular boundary. The eigenmodes are calculated numerically on various examples, and it is shown first that, whatever the shape and characteristic sizes of the boundary, irregularity always induces an increase of localized eigenmodes and a global decrease of the existence surface of the eigenmodes. Besides, irregular cavities are shown to exhibit specific damping properties. As expected, the increased damping, compared to a regular cavity, is related first to the larger perimeter to surface ratio. But more interestingly, there is a specific enhancement of the dissipation for those modes that are localized near the boundary, modes which are favored by the geometric irregularity.