PURPOSE: To obtain echoes of high flaw detecting sensitivity and high measuring accuracy by converging waves at a focal point at the side of a transversal wave oscillator separately provided from a longitudinal wave oscillator and, detecting the echoes of the longitudinal wave+transversal wave by two oscillators.
CONSTITUTION: Longitudinal ultrasonic beams of a piezoelectric element 2b are brought in and refracted with an angle between the critical angles α1 and β2 of the longitudinal and transversal waves by an acoustic lens 3a, turned to transversal waves in a test specimen 6 and converged at the position of a focal point F. Meanwhile, longitudinal ultrasonic beams from a piezoelectric element 2a enter to be refracted with an angle smaller than the angle α1, and converged in the vicinity of the point F inside the test specimen 6 as longitudinal waves, then passing through the test specimen. A focal area F where directional areas 12a, 12b of the ultrasonic beams of the elements 2a, 2b overlap is formed. When a defect exists in the area F, the element 2a detects the longitudinal wave echoes when mainly the longitudinal waves propagate in the test specimen 6. On the other hand, the element 2b detects the transversal wave echoes when the transversal waves propagate in the test specimen 6, as longitudinal wave echoes converted at the surface of the test specimen 6. These two detecting signals are processed to be a defect detecting signal.
MIYATA TORU
SAKUMA NORIMITSU
