| Summary: | 碩士 === 元智大學 === 機械工程學系 === 91 === Ultrasonics has been one of the most popular non-destructive evaluation techniques in resent gears. In this investigation, the ultrasonic C-Scan system is developed. Using the LabVIEW software, the data acquisition and signal process can be easily incorporated and integrated to form an automatically scanning system. There are three main functions included in the C-Scan system: (1) measuring the thickness of a thick specimen and showing the overall profile via the 3-D imaging display; (2) measuring the thickness of a thin film; (3) cross-section inspection examining the cracks, voids or imparities inside a specimen. In order to measure the thickness of a thin film the signals in time domain, which are overlap and unable to obtain the time difference between two echos, are transferred to the frequency domain by Fourier Fast Transform. The reciprocal of the frequency difference between two adjacent local minimum or maximum in frequency domain is equal to the time difference between the reflective waves of top and bottom surfaces. Incorporating the FFT into the C-Scan system to measure the thin film thickness is the most distinctive comparing to the conventional C-Scan. The capability of present C-Scan system is able to measure thickness of 0.5mm for expory and 1mm for aluminum.
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