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Aeronautics composite material inspection with a terahertz time-domain spectroscopy system

: Ospald, F.; Zouaghi, W.; Beigang, R.; Matheis, C.; Jonuscheit, J.; Recur, B.; Guillet, J.-P.; Mounaix, P.; Vleugels, W.; Bosom, P.; Gonzalez, L.; Lopez, I.; Martinez, R.; Sternberg, Y.; Vandewal, M.


Optical engineering 53 (2014), Nr.3, Art. 031208, 15 S.
ISSN: 0091-3286
ISSN: 0036-1860
ISSN: 1560-2303
European Commission EC
Fraunhofer IPM ()
terahertz spectroscopy; composite materials; inspections; time-domain spectroscopy

The usability of pulsed broadband terahertz radiation for the inspection of composite materials from the aeronautics industry is investigated, with the goal of developing a mobile time-domain spectroscopy system that operates in reflection geometry. A wide range of samples based on glass and carbon fiber reinforced plastics with various types of defects is examined using an imaging system; the results are evaluated both in time and frequency domain. The conductivity of carbon fibers prevents penetration of the respective samples but also allows analysis of coatings from the reflected THz pulses. Glass fiber composites are, in principle, transparent for THz radiation, but commonly with significant absorption for wavelengths >1  THz. Depending on depth, matrix material, and size, defects like foreign material inserts, delaminations, or moisture contamination can be visualized. If a defect is not too deep in the sample, its location can be correctly identified from the delay between partial reflections at the surface and the defect itself.