Nondestructive Internal Defect Detection Using Photoacoustic and Self-Coupling Effect

摘要

The demand for noncontact and nondestructive internal defect detection is increasing. Using the photoacoustic effect, internal defects can be detected by a low-power semiconductor laser and an ultrasonic sensor. But the sensitivity of ultrasonic sensors is low in detecting photoacoustic signals. Thus, an internal defect detection using the photoacoustic and self-coupling effect of a semiconductor laser has been studied. To generate photoacoustic signals, a semiconductor laser with an output power of 20 mW is focused by a lens and is directed toward the sample at an angle of 45°. To detect the photoacoustic signal by the self-coupled effect, another laser with an output power of 10 mW is directed against the sample at a right angle. Sample defect can be detected by directing these laser beams at the same point on the sample. The self-coupling sensor can detect internal defects with greater sensitivity than an ultrasonic sensor. The edge effect and the frequency characteristic have also been observed. The device proved able to detect a very small defect of 0.07 mm.