DETECTION OF ECHOES USING TIME-FREQUENCY ANALYSIS TECHNIQUES

The following is a presentation of echo detection techniques based on time-frequency signal analysis for the measuring of thickness in thin multilayer structures, These techniques are shown to provide high-reso lution signal characterization in a time-frequency space, and good noi se rejection performance, In particular, the Short-Time Fourier Transf orm, the Gabor expansion, the Cross-Ambiguity Function and the Wigner- Ville Distribution are analyzed and compared with techniques such as t he logarithmic power spectrum, Cepstrum and the Segmented Chirp Z-Tran sform. A suitable operating procedure was set up, based on an initial emulation phase in which simulated signals were considered, followed b y a second phase in which real signals were processed, The results sho w the optimum performances of these new techniques compared with the t raditional ones and, in particular, that the accurate measurement of t hickness can be obtained also when waveform transients partially overl ap.