Description of a method for the measurement of the Rayleigh wave velocity: application to the thickness measurement of metallic coatings

The velocity of leaky Rayleigh waves, generated by a special transducer immersed in water, were calculated from the measurement of the phase φ as a function of the transducer distance z to the specimen surface in the adequate z range. A model, predicting the theoretical φ(z) curve, permitted the choice of this z range. The technique proposed was then applied to metallic coatings deposited on steel substrates in order to measure their thickness. In fact, in layered media, the Rayleigh wave velocity is a function of the product of the layer thickness by the wave frequency