Nondestructive internal defect detection using photoacoustic and self‐coupling effect

Abstract

AbstractThe 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. © 2010 Wiley Periodicals, Inc. Electron Comm Jpn, 93(7): 17–23, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10307