Leaky Rayleigh Waves in the Presence of Loading and Stiffening Layers

Abstract

The distortion and displacement of a finite-aperture acoustic wave incident from a fluid onto a fluid-solid interface at or near the Rayleigh critical angle is phenomenon which has received considerable attention recently1–5. Physically, resonant generation of Rayleigh-like waves and rapid reradiation of the surface-wave energy into the fluid are responsible for the characteristic displacement and distortion of the acoustic beam. These effects typically lead to a bimodal reflected acoustic field, composed of a remnant specular reflection summed coherently with the radiating surface wave. When conditions of beam width and wavelength are favorable, a portion of the field distribution shows a strong reduction in amplitude, due to the phase cancellation of component fields. The sensitivity of this null zone to surface condition (including the presence of coatings) suggests that a NDE technique may be based on this effect. The situation is illustrated schematically in Fig. 1. An acoustic beam incident at the Rayleigh angle suffers displacement and distortion with most of the power contained in the shaded regions. The suppressed specular reflection is indicated by the dashed lines.