DETECTION OF ECHOES IN NOISY ENVIRONMENTS FOR MULTILAYER STRUCTURE CHARACTERIZATION

This paper deals with digital signal processing techniques set up to d etect echoes in noisy environments and to thus carry out thickness mea surements in thin multilayer structures. In particular, the Cepstrum a nd the Segmented Chirp Z-Transform are analyzed and compared, highligh ting their performances in relation to noise characteristics. A suitab le operating procedure was set up, based on an initial emulation phase in which simulated signals are considered, followed by a second phase in which real signals are processed. The results show that optimum pe rformances can be achieved by using the Segmented Chirp Z-Transform to gether with a high flexible window.