Effects of a default on the reflectivity of plane periodic media

Olivier Lenoir (1) , Aissam Khaled , Pierre Marechal (1) , Driss Chenouni (2)

1 LOMC - Laboratoire Ondes et Milieux Complexes
2 LESSI

The influence of defect layers in a fluid-loaded plane multilayer composed of N periods is highlighted by analyzing the stop bands and pass bands of the reflection coefficient. The period is composed of two plates exhibiting a high impedance contrast, in aluminum and polyethylene for instance. No attenuation is taken into account Two types of defect layers are considered: either the thickness of a plate in one period is varied, or a layer made up of another material is inserted between two adjacent periods. The transmission coefficient is obtained with a numerically stable transfer matrix method. The study consists in comparing the plots of the transmission coefficient of a structure with no defect to the ones of structures with defects inserted at different locations. The variations of the resonance frequencies in the pass bands according to the defect position, as well as the width of the stop bands, are studied. A particular attention has been paid to the resonances at low frequency, linked with the so-called vertical modes. In the case of a defect included between two periods, it may appear very narrow pass bands in the stop bands.

Mots clés: periodic media; resonances; pass bands; modes

Domaines: Acoustique [physics.class-ph]

Olivier Lenoir, Aissam Khaled, Pierre Marechal, Driss Chenouni. Effects of a default on the reflectivity of plane periodic media. Acoustics 2012, Apr 2012, Nantes, France. ⟨hal-00810868⟩