Validation of analytically modeled Leaky Lamb radiation using Schlieren photography

If a guided Lamb wave leaks energy from a plate into a surrounding fluid, the radiated almost plane wave has a frequency dependent angle towards the boundary. This radiation angle can be calculated by numerical determination of the plates´ phase velocities. We also measured the radiation angle in Schlieren photographs and found a mentionable discrepancy to the calculated angles in certain frequency regions. A first approach by modifying the boundary condition could not resolve the observed discrepancies, but a reinterpretation of the Schlieren photographs as interference patterns of different Leaky Lamb waves leads to a good correspondence between measured and calculated values.