Splitting of domain of angles for incident wave vectors in elastic anisotropic media

Abstract

An anomalous phenomenon in the reflection and refraction of elastic waves on an interface between anisotropic crystals is analyzed. Due to the deviation of the ray (energy flow) direction from the wave normal for elastic waves in crystals, the domain of permissible incident angles splits into disjoint pieces for certain crystal cuts. This may lead to the existence of grazing angles at three different wave-vector angles. The grazing angle is defined as the angle at which the ray vector of the incident wave is parallel to the interface. To clarify this interesting phenomenon, numerical calculations were made for the (001) plane of a Ni crystal, based on a calculational procedure developed previously for study of the reflection and refraction of elastic waves in crystals. For each of the two split domains of incident angle there appear two branches of the reflection coefficient for the slow quasi-transverse wave corresponding to the same slowness surface. The value of the energy conversion of the incident wave into each of these reflected waves depends on the closeness of the direction of the displacement vector in these waves to the incident displacement direction.