Backward displacement of ultrasonic waves reflected from a corrugated interface

Abstract

A backward displacement can occur when an ultrasonic beam is reflected from an interface having a superimposed periodicity. This was first observed by Breazeale and Torbett [Appl. Phys. Lett. 29, 456 (1976)]. They observed that at a certain critical angle the reflected beam was shifted at 6 MHz and not at 2 MHz, in agreement with the theory of Tamir and Bertoni [J. Acoust. Soc. Am. 61, 1397–1413 (1971)]; however, the angle predicted by assuming that the shift was caused by a Rayleigh surface wave did not agree with experiment. Recent experiments using the schlieren technique showed backward displacement at an incident angle of 25 deg, in good agreement with the value 23.69 deg calculated using the inhomogeneous wave theory [Briers et al., J. Acoust. Soc. Am. 106, 682–7 (1999) (private communication with N. F. Declercq)]. The inhomogeneous wave theory also predicts a new kind of leaky surface wave at an incident angle of 22.55 deg [N. F. Declercq (private communication)], again in agreement with our measurements. Schlieren photographs of the backward-displaced beams at a water-brass interface are presented and discussed, as is the effect of the presence of an evanescent wave at the interface.