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Proceedings Paper

Potential and limitations of eddy current lockin-thermography
Author(s): G. Riegert; A. Gleiter; G. Busse
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Paper Abstract

Eddy current thermography uses an induction coil to induce eddy currents in conductive materials. The involved resistive losses heat the sample. By modulation of the eddy current amplitude, thermal waves are generated which interact with boundaries thereby revealing defects. Conventional eddy current testing has only a limited depth range due to the skin effect of metal samples. In Induction-Lockin-Thermography (ILT) the depth range is extended by the thermal penetration depth. An infrared camera monitors the modulation of the temperature field on the surface as a response to the coded excitation thereby allowing for fast imaging of defects in larger areas without the need of slow point-by-point mapping. This response is decoded by a Fourier analysis at the modulation frequency. So the extracted information is displayed by just two images where one displays local amplitude and the other local phase. ILT has significant advantages as compared to inductive heating with visual inspection of the thermographic sequence: Phase angle images are independent of most artifacts like reflections, variation in emission coefficient, or inhomogeneous heating. Due to the performed Fourier analysis of the temperature image sequence, the signal-to-noise ratio in the amplitude and phase images is significantly better than in single temperature images of the sequence. Induction heating is confined to conductive materials. However, it is applicable not only to metals but also to carbon fiber reinforced laminates (CFRP) or carbon fiber reinforced ceramics (C/C-SiC). The presented examples for applications of ILT illustrate the potential and limitations of this new non-destructive inspection method.

Paper Details

Date Published: 18 April 2006
PDF: 8 pages
Proc. SPIE 6205, Thermosense XXVIII, 62051E (18 April 2006); doi: 10.1117/12.662716
Show Author Affiliations
G. Riegert, Univ. of Stuttgart (Germany)
A. Gleiter, Univ. of Stuttgart (Germany)
G. Busse, Univ. of Stuttgart (Germany)

Published in SPIE Proceedings Vol. 6205:
Thermosense XXVIII
Jonathan J. Miles; G. Raymond Peacock; Kathryn M. Knettel, Editor(s)

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