Detection of echoes in noisy environments for multilayer structure characterization

Digital signal processing techniques set up to detect echoes in noisy environments and to thus carry out thickness measurements in thin multilayer structures are discussed. In particular, the cepstrum and the segmented chirp Z-transform are analyzed and compared, highlighting their performances in relation to noise characteristics. A suitable operating procedure was set up, based on an initial emulation phase in which simulated signals are considered, followed by a second phase in which signals were processed. The results show that optimum performances can be achieved by using the segmented chirp Z-transform together with a high flexible window.>