Anomalies in the dispersion of guided waves in a fluid-loaded periodic corrugated plate

Results of experimental measurements of ultrasonic leaky Lamb waves and Scholte-Stoneley waves in an immersed plate with a periodic profile are presented. Plate modes and surface modes are generated on a thin fluid-coupled plate due to diffraction and mode conversion on the periodic grooves engraved on the metallic sample. A significant advantage of such a method is its ability to excite guided waves that have a phase velocity lower than the velocity of the fluid. Sharp dips observed in the reflected spectrum at certain frequency positions are related to the existence of Lamb and Scholte-Stoneley modes. Special emphasize is given to the low frequency domain. Experimental data show anomalous ultrasonic dispersion in this region and a mixing between the A₀ mode and the Scholte-Stoneley mode