Rayleigh waves are influenced most by defects located

• A. 6 wavelengths below the surface
• B. Close to or on the surface
• C. 1 wavelength below the surface
• D. 3 wavelengths below the surface

Answer: (B)

Rayleigh waves are surface-bound ultrasonic waves whose energy and particle motion are concentrated in the near-surface region and decay with depth. Because most of the wave energy resides within a shallow depth from the surface, flaws that are right at the surface or very close to it interact most strongly with the wave, producing the largest detectable changes in the signal. Defects deeper in the material receive less Rayleigh-wave energy, so their influence is weaker. This makes surface or near-surface defects the ones Rayleigh waves are most sensitive to, which is why the option describing flaws located close to or on the surface is the best choice.