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The ultrasonic backward beam displacement, which has been shown to occur when a bounded beam is incident upon a periodically corrugated liquid-solid interface, is studied experimentally. This effect has been previously studied on a periodic water-brass interface at one particular frequency (6 MHz) and one corresponding angle of incidence (22.5 degrees), but the question has remained whether it would also exist at other frequency and angle combinations. The knowledge of whether this phenomenon is a coincidence or whether it will occur for other frequency and angle combinations contributes to a better understanding of the interaction of ultrasound with periodic structures and diffraction effects, in particular. Potential applications exist in the study of phononic crystals and in the non-destructive evaluation of materials. The present work reports results from recent experiments on the same periodically grooved brass sample that was employed in the first investigations of this phenomenon. Through the examination of frequency spectra in the form of angular and classical spectrograms, the experiments reported here show the backward beam displacement to occur for multiple angles of incidence and frequencies. Furthermore, evidence is shown as to the exact cause of the backward beam displacement, namely, a backward propagating Scholte-Stoneley wave.

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Current theory applied to ultrasonic diffraction from periodically corrugated surfaces is valid only in the far-field; it cannot be applied to determine the diffracted field within the surface corrugations themselves. Therefore, information regarding the corrugation is difficult to extract from experiments that are necessarily conducted in the far-field. The present work aims to simulate a potential experimental method for investigating the corrugations themselves. Using near-field results obtained from a finite-element code, the far-field diffraction is constructed as a series of time-harmonic plane waves. By back-propagating this diffracted field, information about the corrugations is obtained. Comparing the results of the back-propagated field to the field generated by the finite-element code shows the limitations of determining details of periodically corrugated surfaces from far-field experiments.