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Proceedings Paper

Fuselage inspection of Boeing-737 using lock-in thermography
Author(s): Markus Tarin; André Kasper
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Paper Abstract

Optically modulated elastic waves enter the surface of the inspected material by absorption of thermal radiation. An inhomogeneous disturbance in the material causes locally enhanced losses. Such material defects heat up at a different rate than the surrounding more homogenous material and therefore generate differences in thermal contrast. Modulating the amplitude of the optical stimulus turns defects into thermal wave transmitters. The frequency of the stimulus signal must be matched to the specific thermal conductivity and mass density of the inspected material. It is possible to locate defects at different depths below the surface by varying the amplitude of the stimulus wave. Proper detection of thermal waves resulting from material defects near the surface requires a measurement setup that allows the recording of thermal images from an infrared camera. The recorded images can then be compared against the phase of the stimulus signal. This photo-thermal lock-in thermography method not only allows the evaluation of the amplitudal thermal wave information but more importantly it also allows for the extraction of the phase information. The phase shift between the stimulus signal and the captured thermal wave is directly correlated to the thermal propagation time.

Paper Details

Date Published: 17 March 2008
PDF: 10 pages
Proc. SPIE 6939, Thermosense XXX, 693919 (17 March 2008); doi: 10.1117/12.777008
Show Author Affiliations
Markus Tarin, MoviMED (United States)
André Kasper, Automation Technology GmbH (Germany)

Published in SPIE Proceedings Vol. 6939:
Thermosense XXX
Vladimir P. Vavilov; Douglas D. Burleigh, Editor(s)

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