A0 mode interaction with a plate free edge: Theory and experiments at very low frequency by thickness product

When a plane acoustic wave reaches a medium with an impedance infinite or null, it experiences a phase shift of zero or π and its amplitude on the edge is maximum or vanishes. The case of a flexion wave (A0 Lamb wave) at a free end is also simple; its amplitude is multiplied by a factor 22 and the phase shift is π∕2. The evanescent wave at the origin of these phenomena, perfectly described by the classical flexural plate theory, is identified as the imaginary A1 mode of the exact Rayleigh-Lamb theory. The experiences confirm the theoretical predictions.