Patent attributes
A flaw Z with a long probing length inside a probing target is allowed to be probed. The waves other than the probing target waves are removed or reduced, so that the individual difference in the sizing result due to the ability of the measuring personnel is eliminated to improve the precision of the probing. A transmission probe 31 and a receiving probe 32 for transmitting and receiving a wide band ultrasonic wave are included. Each time the positions of the probes 31 and 32 are moved, a received wave Gj(t) is obtained. From a spectrum Fj(f) corresponding to the received wave Gj(t), a narrowband spectrum FAj(f) is extracted. A component wave GAj(t) corresponding to the narrow band spectrum FAj(f) is obtained by inverse Fourier transformation. The component wave GAj(t) is provided for a comparative display using a predetermined sizing coefficient. The position of a flaw Z is determined inside a probing target 30 right below the line segment connecting the centers of the transmission probe 31 and the receiving probe 32, based on at which of the measurement points a wave is generated on the comparative display screen.
