Backward displacement of waves reflected from an interface having superimposed periodicity

An ultrasound beam incident on a liquid-solid interface with superimposed grating is shown to be displaced in a backward direction at certain angles of incidence predicted by the theory of T. Tamir and H. L. Bertoni [J. Opt. Soc. Am. 61, 1397–1413 (1971)]. The analogy between the ultrasonic phenomenon and the corresponding optical phenomenon is cited.