UT Testing-Section 2 Physics of Ultrasound

Since the 1990s, the understanding and utilization of lamb waves has
advanced greatly, thanks to the rapid increase in the availability of computing
power. Lamb's theoretical formulations have found substantial practical
application, especially in the field of nondestructive testing.
The term rayleigh–lamb waves embraces the rayleigh wave, a type of wave
that propagates along a single surface. Both rayleigh and lamb waves are
constrained by the elastic properties of the surface(s) that guide them.
http://en.wikipedia.org/wiki/Lamb_wave
http://pediaview.com/openpedia/Lamb_waves