On the crossing points of the Lamb modes and the maxima and minima of displacements observed at the surface.

Highlights: [•] Maximum and minimum of the surface displacements of Lamb waves is discussed. [•] Location of the vanishing displacements is predicted by the crossing of the bounds. [•] Experimental influence is demonstrated by a laser-ultrasonic technique. [•] Periodic variation of the maximum and minimum is predicted. [ABSTRACT FROM AUTHOR]