Suppressing Technique of the Antisymmetric Mode by the Superposition of Lamb Waves Generated by Two Laser Beams in a Thin Plate

We present a suppressing technique of the antisymmetric mode by superposition of Lamb waves generated by two laser beams in a thin plate. Two Lamb waves of the same frequency propagating from the opposite direction simultaneously arrive at the point of measurement and are superposed to compose one Lamb wave. The amplitude of the superposed Lamb wave depends on the distance between two laser beams. The suppressing of antisymmetric Lamb wave mode is accomplished by selecting the distance between two beams which simultaneously satisfies the condition of the anti-node(maximum) for the symmetric mode and the minimum for the antisymmetric mode. By this method, the antisymmetric Lamb wave mode is suppressed to the degree of 1.4% of the amplitude measured at zero distance between two beams.