Existence of zero-group velocity modes in an incompressible plate

Zero-group velocity (ZGV) Lamb modes are studied in an incompressible orthotropic plate. The existence of such modes critically depends on the anisotropy parameter a = ( c 11 + c 22 − 2 c 12 − 4 c 66 )/ c 66 . With materials having a > −1, none of the modes possesses any ZGV points and every mode has such a point if a < −1. Several modes have multiple ZGV points.