Abstract
We have proposed an ultrasonic computerized tomography method using the time-of-flight (TOF) of a longitudinal wave as a defect detection method for a steel billet. However, it took a long time to measure the TOFs because the transmissions were made one by one from the requirement of independent signal transmission. In this study, to speed up the TOF measurement, we proposed a simultaneous measurement method of TOFs using the phase-modulated signals by Gold sequences, and evaluated the ability of simultaneous measurement by an experiment. The reflected wave from the billet surface had a very adverse effect on the measurement of TOF, so a short signal was required as the transmitted signal. To make the transmitted signal short, a half-sine pulse phase-modulated by a Gold sequence was employed. As a result, five simultaneous transmissions were possible to be used for the inspection of the billet. When five simultaneous transmissions are made, the total measurement time can be decreased to 1/5 of the previous one.