Claire Prada (Institut Langevin, Paris). Negative phase velocity and zero group velocity elastic guided modes in simple media.

Elastic wave guides support the propagation of modes with peculiar dispersion properties resulting from the coupling of shear and compression waves. Notably, negative phase velocity or backward modes can propagate in most homogeneous wave guides. Moreover, in the absence of attenuation or leakage, a backward mode dispersion branch is linked to a zero group velocity (ZGV) mode which is associated to a narrow and local resonance.  Through several laser ultrasonics and array imaging experiments, I will describe the remarkable properties of these modes and some related effects as negative refraction and negative reflection in plates, or backscattering enhancement from shells. I will also present some applications of ZGV modes to non-destructive evaluation.