Relation between the Phase of the Reflected Ultrasound and the Thickness of a Thin Layer Placed on a Solid Halfspace

摘要

In the past, several authors [1-12] studied the reflection and transmission of plane waves through layered media. Detailed information of the most general case of wave propagation in a thin solid layer welded to an infinite substrate is given in references [6, 9]. The aim of the research presented in this paper is to make a study of the dependence of the reflection coefficient on the thickness of a thin layer placed upon a solid halfspace. From the theory of Brekhovskikh [I], it is seen that for a thin layer -of thickness much smaller than the ultrasonic wavelength - the dependence of the modulus of the reflection coefficient on the thickness is small and immeasurable. Also Wevers [13] mentions this phenomenon in a survey of non-destructive inspection techniques for advanced composites (composed of several fibre-reinforced layers). However taking into account the phase information of ultrasonic reflections from disbonds in layered structures, such defects can be measured more accurately.