Backward displacement of ultrasonic waves reflected from a periodically corrugated interface

Experiments using the schlieren technique to image sound incident on a corrugated, water-brass interface show a backward displacement of the reflected beam at an angle of 22.5°, confirming the observations of Breazeale and Torbett [ Appl. Phys. Lett. 29 , 456 ( 1976 ) ]. However, the present theory hypothesizes that this beam displacement results from excitation of a type of leaky surface wave. Further experiments with a sufficiently narrow incident beam reveal a backward displacement also at angles around 44°, resulting from excitation of Rayleigh surface waves, as predicted by the theory of Tamir and Bertoni [ J. Acoust. Soc. Am. 61 , 1397 ( 1971 ) ]. Thus, a wide beam gives a backward displacement at 22.5° only. A narrow beam gives a backward displacement also at angles around 44°.