SUMMARY

The study of the interaction of acoustic and elastic waves with periodic surfaces and structures has a rich history dating back to Lord Rayleigh, and it has been recently attracting new research efforts due to its value in the study of phononic crystals and in methods for ultrasonic non-destructive evaluation (NDE). The objective of this proposed PhD thesis research is to extend current knowledge of acoustic and elastic wave diffraction effects on structures having periodically corrugated surfaces using both theoretical and experimental methods and within the framework of ultrasonic NDE. The proposed research is divided into three main parts. First, the Rayleigh-Fourier (R-F) method will be used to simulate diffracted fields generated by structures containing multiple periodic surfaces and/or multiple solid layers. Because theoretical simulations such as those performed with the R-F method are often restricted to the case of “ideal” periodic surfaces having perfect periodicities rather than “real” surfaces with imperfect periodicities that would more likely be encountered in practice, a second part of this proposed thesis research will consist of experiments to study diffraction effects for surfaces with imperfect periodicities. The final portion of this proposed PhD thesis research will focus on one unusual phenomenon that has been observed on periodically corrugated surfaces, namely the lateral backward displacement of a bounded ultrasonic beam along the surface. This effect is currently understood to occur due to backward propagating surface waves that result from diffraction and mode conversion on the surface. However, this phenomenon has only been observed for time-harmonic waves in reflection. Since ultrasonic NDE methods often employ pulses, this phenomenon will be studied experimentally for the case of ultrasonic pulses in reflection as well as in transmission.