Section 2: Physics of Ultrasound

Surface wave or Rayleigh wave are formed when shear waves refract to 90.
The whip-like particle vibration of the shear wave is converted into elliptical
motion by the particle changing direction at the interface with the surface. The
wave are not often used in industrial NDT although they do have some
application in aerospace industry. Their mode of propagation is elliptical along
the surface of material, penetrating to a depth of one wavelength. They will
follow the contour of the surface and they travel at approximately 90% of the
velocity of the shear waves.
Depth of penetration of
about one wavelength
Direction of wave propagation