Application of time delay spectrometry for rough surface characterization

This paper describes the design and performance of an ultrasound measuremen t system, utilizing a swept frequency excitation signal, for analyzing the backscattered signal from planar rough surfaces. The implementation is in t he form of a time delay spectrometry (TDS) system operating in reflection m ode whose advantages are improved signal-to-noise ratio even with low peak power relative to conventional pulse-echo methods. Because of simultaneous transmission and reception, the TDS system requires two transducers. The TD S measurement system uses a swept frequency spectrum analyzer as the centra l analog processing unit. Both planar piston and focused transducers in the low MHz range were used for the measurements. Due to the statistical natur e of rough surface backscatter, the mean of several statistically uncorrela ted measurements is required to characterize the scattering behavior of a g iven rough surface. Backscatter data are obtained for a series of planar ro ugh surfaces, in the form of scattering magnitude vs, frequency and vs. inc ident (=backscattered) angle. Analysis of the results reveals a good correl ation between the root-mean-square (RMS) height and mean backscatter magnit ude at 0 degrees incident angle, and between the ratio of RMS height to cor relation length and the difference in mean backscatter magnitude between 0 degrees and 5 degrees. (C) 2001 Elsevier Science B.V. All rights reserved.