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Proceedings Paper

Spatial and temporal control of thermal waves by using DMDs for interference based crack detection
Author(s): Erik Thiel; Marc Kreutzbruck; Mathias Ziegler
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Paper Abstract

Active Thermography is a well-established non-destructive testing method and used to detect cracks, voids or material inhomogeneities. It is based on applying thermal energy to a samples’ surface whereas inner defects alter the nonstationary heat flow. Conventional excitation of a sample is hereby done spatially, either planar (e.g. using a lamp) or local (e.g. using a focused laser) and temporally, either pulsed or periodical. In this work we combine a high power laser with a Digital Micromirror Device (DMD) allowing us to merge all degrees of freedom to a spatially and temporally controlled heat source. This enables us to exploit the possibilities of coherent thermal wave shaping. Exciting periodically while controlling at the same time phase and amplitude of the illumination source induces – via absorption at the sample’s surface - a defined thermal wave propagation through a sample. That means thermal waves can be controlled almost like acoustical or optical waves. However, in contrast to optical or acoustical waves, thermal waves are highly damped due to the diffusive character of the thermal heat flow and therefore limited in penetration depth in relation to the achievable resolution. Nevertheless, the coherence length of thermal waves can be chosen in the mmrange for modulation frequencies below 10 Hz which is perfectly met by DMD technology. This approach gives us the opportunity to transfer known technologies from wave shaping techniques to thermography methods. We will present experiments on spatial and temporal wave shaping, demonstrating interference based crack detection.

Paper Details

Date Published: 15 March 2016
PDF: 13 pages
Proc. SPIE 9761, Emerging Digital Micromirror Device Based Systems and Applications VIII, 97610N (15 March 2016); doi: 10.1117/12.2210918
Show Author Affiliations
Erik Thiel, Bundesanstalt für Materialforschung und -prüfung (Germany)
Marc Kreutzbruck, Univ. Stuttgart (Germany)
Mathias Ziegler, Bundesanstalt für Materialforschung und -prüfung (Germany)

Published in SPIE Proceedings Vol. 9761:
Emerging Digital Micromirror Device Based Systems and Applications VIII
Michael R. Douglass; Philip S. King; Benjamin L. Lee, Editor(s)

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