It 's actually with some considerable apprehension that I address this audience. I will try to alleviate my apprehension somewhat by telling you right at the outset that I do not have a single data slide showing a detected flaw. What's more I have to confess, I have never detected a flaw. I sincerely hope you'll forgive me for this. My apprehension is heightened by my observation over the last several days that there is very little interest in ultrasonic work at the frequencies that are of interest to me, the range of about 1 to 10 GHz. I don't think I've heard anything over 1 GHz mentioned. Perhaps it's becoming apparent to most of you that I am not principally in nondestructive evaluation. What I am interested in is lattice dynamics; more specifically relaxation effects in dielectric solids.