Abstract
To reduce the intensity of artifacts in visualized images for detecting defects in square billets by ultrasonic computerized tomography, we propose a method, which utilizes the crosspower-spectrum phase (CSP) function between a measurement signal and a reference signal, to measure the time-of-flight (TOF) difference. The artifacts arise owing to measurement errors of the TOF difference, which are caused by the effects of propagation characteristics and side lobes in correlation waveforms. The effects of propagation characteristics may be reduced using the reference signal, which contains the same characteristics as those of the measurement signal. The side lobes in correlation waveforms may also be decreased using the CSP method. The results obtained by experiment suggest that the intensity of artifacts was reduced because the proposed method reduced the side lobe level by about -14 dB and the number of measurement errors. The visualized images showed that the defects whose diameter was more than 2.0 mm were detected using the input signal whose wavelength was in the range from 2 to 6 mm.
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