High-sensitivity laser-based ultrasonic C-scan system for materials inspection |
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Authors: | F Lanza di Scalea R E Green Jr |
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Institution: | (1) Department of Structural Engineering, University of California, San Diego;(2) Center for Nondestructive Evaluation, The Johns Hopkins University, 21218 Baltimore, MD |
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Abstract: | A beam-steering C-scan system for laser generation and detection of ultrasound in opaque solids has been developed. For ultrasound
detection, the system uses a confocal Fabry-Perot interferometer that is stabilized at its high-sensitivity point by implementing
a novel procedure that does not require a reference beam. This stabilization procedure effectively compensates for slowly
varying (up to 2 Hz) disturbances and, more important, for any change in the interferometer illumination conditions while
probing different scanning points. For the latter reason, the proposed stabilization appears to be more effective than previous
approaches for high-sensitivity ultrasound detection in beamsteering scans. Noise performance and sensitivity limit of the
system are evaluated. Ultrasonic echoes are detected in aluminum samples having optically rough surfaces with single-pulse
generation signal-to-noise ratios on the order of 20 dB. A C-scan inspection is performed where a known defect in the test
piece is successfully detected by time-of-flight gating of the ultrasonic signals. |
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Keywords: | Laser ultrasonics Fabry-Perot interferometer C-scan test |
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