| 摘要 |
PURPOSE:To detect a defect existing near the surface of an object to be inspected satisfactorily, by making an ultrasonic beam incident into the surface thereof with the frequency being varied by several stages to measure and compute surface echoes and combined echoes at respective frequencies. CONSTITUTION:A vertical probe 1 is kept in contact with the surface A without defects of an object 3 to be inspected and an ultrasonic beam is made incident thereinto, for example, at 3MHz. Consequently, a surface echo 7 is reflected with the height thereof being Ps. Then, when an ultrasonic beam is made incident into the surface B with defects, a cominbed echo of the surface echo 7 and a defect echo 6 is reflected with the height being Ph. The frequency of the ultrasonic beam is shifted to 30MHz and the same operation is done to determine the height P's of the surface echo at a point without any defect and the height P'h of te combined echo at a point with defects. As the echo heights Ps, Ph, P's and P'h are in a correlation with the distance and size of the defect, an arithmetic control section 13 performs a computation to detect the location and size of the defect. Therefore, the defect can be detected, at a high accuracy as the echo height is determined by varying the ultrasonic frequency. |
