A type of ultrasonic wave propagation in which the wave is guided between two parallel surfaces of the test object. For an object sufficiently thin to allow penetration to the opposite surface, e.g. a plate having a thickness of the order of a wavelenght or so, Rayleigh waves degenerate to Lamb waves, which can be propagate in a number of modes, either symmetrical or antisymmetrical . The velocity is dependent on the product of frequency and material thickness. Lamb waves are named for Horace Lamb, in honor of his fundamental contributions to this subject. Investigation on Lamb and leaky Lamb waves have been carried out continuously since their discovery and researchers have done theoretical and experimental work for different purposes, ranging from seismology and the ship construction industry to acoustic microscopy, non-destructive testing and acoustic sensors.
Synonymous terms are guided wave and plate wave .