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Optimized temporal excitation profiles in active thermography

: Netzelmann, U.

Analytical sciences. The international journal of the Japan Society for Analytical Chemistry 17 (2001), Special Issue, S.s432-s435
ISSN: 0910-6340
International Conference on Photoacoustic and Photothermal Phenomena <11, 2000, Kyoto>
Zeitschriftenaufsatz, Konferenzbeitrag
Fraunhofer IZFP ()
coating thickness; thermographisches Prüfverfahren

The thermal response of opaque coatings after heating with pulses of finite duration is analyzed theoretically with respect to detection of small variations of the coating thickness. Rectangular shaped heating pulses and step pulses with exponential decay are considered. The investigation is based on existing analytical solutions for step-function heating and for delta-pulse heating. For the exponentially decaying pulse, a numerical convolution is performed. For the rectangular pulse, the best sensitivity for thickness variations (thickness contrast) is generally obtained 0.2 to 0.9 Fo-numbers after the end of the pulse. A good selection for the pulse length is 0.5 to 1.5 Fourier numbers of the coating. For the exponentially decaying pulse, the maximum thickness contrast is smaller than for the rectangular pulse and easily hidden by disturbing radiation. Experimental realization of rectangular short pulses is approximately possible by switched flash lamps.