Zero Group Velocity and backward Lamb modes

Abstract : Laser ultrasonics techniques are very useful to investigate Lamb modes in plates. In this talk, the remarkable properties of zero group velocity (ZGV) and backward Lamb modes will be discussed and illustrated through measurements done with nanoseconds laser ultrasonics. These modes originate from the repulsion between two dispersion branches having close cut off frequencies, corresponding to a longitudinal and a transverse thickness mode of the same symmetry. The lowest branch exhibits a minimum corresponding to the ZGV mode and a negative slope associated to backward propagation. The frequency spectrum of the plate elastic response to a local impact is entirely dominated by ZGV resonances and for isotropic plates the set of resonance frequencies provides an accurate measurement of the local Poisson's ratio. When either the transverse or the longitudinal acoustic velocity is known, plate thickness can be precisely determined. Backward modes, having negative phase velocities, exist in the vicinity of a ZGV mode. It will be shown that mode conversion from the S2 forward mode to the S2b backward mode can be achieved at a plate thickness change. Then, negative refraction and focusing can be obtained with a simple flat lens.
Type de document :
Communication dans un congrès
Société Française d'Acoustique. Acoustics 2012, Apr 2012, Nantes, France. 2012
Liste complète des métadonnées
Contributeur : Hal System <>
Soumis le : lundi 23 avril 2012 - 10:00:00
Dernière modification le : vendredi 4 janvier 2019 - 17:33:27
Document(s) archivé(s) le : dimanche 18 décembre 2016 - 13:06:43


Fichiers éditeurs autorisés sur une archive ouverte


  • HAL Id : hal-00811250, version 1


Claire Prada, Franck Philippe, Dominique Clorennec, Maximin Cès, Daniel Royer. Zero Group Velocity and backward Lamb modes. Société Française d'Acoustique. Acoustics 2012, Apr 2012, Nantes, France. 2012. 〈hal-00811250〉



Consultations de la notice


Téléchargements de fichiers