Generalized Snell's law and its possible relation to coherent backscattering of ultrasonic waves

摘要

The cause of backscattering in the Rayleigh angle has first been explained by means of finite beam models in which there are inherently present backward traveling components that explain the backscattering effect. Later, the nature of backscattered sound was proved to consist mostly of incoherent sound due to material anomalies. The present work shows that besides the well known real Snell's law: i.e., continuity of the frequency and continuity of the wave vector component along the interface, there is also the possibility of a complex solution of Snell's condition of continuity. The latter shows that it is possible that a part of the incident sound gets reflected into nonspecular directions including the backscatter direction. Furthermore, it is shown that this sound must have a different frequency than the incident frequency.