Abstract-Ageing Condition Determination of Bonded Joints by Terahertz Spectroscopy

Jochen Taiber, Martin Kahlmeyer, Andreas Winkel, Eva-Maria Stübling, Fatima Taleb, Mikhail Mikerov, Stefan Sommer, Stefan Böhm, Martin Koch

https://www.springerprofessional.de/en/ageing-condition-determination-of-bonded-joints-by-terahertz-spe/18206724

The understanding of ageing processes in the field of adhesion technology is of utmost importance for long-term durable bonded joints. Environmental factors such as moisture, heat and UV radiation negatively affect the characteristics of adherends, adhesives and their interfaces and thus the overall bond performance over time. However, the evaluation of the precise ageing condition of adhesive joints remains challenging by means of well-established non-destructive testing (NDT) methods like shearography or thermography. Recently, it has been shown that terahertz (THz) time-domain spectroscopy is well suited as an NDT approach to study adhesive bonds. Specialized data extraction schemes enable the contact-free determination of the refractive index and the absorption coefficient from such measurements. The presented work wants to give an overview on the developments in the application of THz spectroscopy for the ageing condition determination of bonded joints, including the correlation between THz refractive index/absorption and the physical, chemical and mechanical property changes of adherends and adhesives due to ageing, the determination of THz specific values of adhesive joints by means of a reflection setup, the suitability of peak-to-peak amplitude evaluation, and THz imaging

Abstract-THz tomography for detecting damages on wood caused by insects

Kirsti Krügener, Eva-Maria Stübling, Roksana Jachim, Bettina Kietz, Martin Koch, and Wolfgang Viöl

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-58-22-6063

Annually, wood-destroying insects cause severe damage in forests. The widespread population of typographer (Ips typographus), a beetle species from the subfamily of bark beetles (Scolytidae) in Europe, mainly occurs in coniferous wood, especially in spruce (Picea abies), the most silviculturally relevant wood species. The typographer infestation is detected mainly by visual monitoring and without invasive techniques only recognizable at a late stage. Terahertz radiation has shown enormous potential in nondestructive testing. THz measurements in the time-domain performed with a robotic THz system can be used for 3D reconstruction of the internal structure of the samples. In this article, we report the detection of a change in the wood structure of spruce caused by typographer burrows.

© 2019 Optical Society of America

Abstract-Application of a robotic THz imaging system for sub-surface analysis of ancient human remains

Eva-Maria Stübling, Arno Rehn, Tabea Siebrecht, Yannick Bauckhage, Lena Öhrström, Patrick Eppenberger, Jan C. Balzer, Frank Rühli, Martin Koch,

https://www.nature.com/articles/s41598-019-40211-7

We used a robotic-based THz imaging system to investigate the sub-surface structure of an artificially mummified ancient Egyptian human left hand. The results obtained are compared to the results of a conventional CT and a micro-CT scan. Using such a robotic THz system promises new insights into the sub-surface structure of human remains. The depth resolution of the THz images exceeds the resolution of a conventional CT scan and is comparable with a micro-CT scan. The advantage of THz measurements over micro-CT scans is the fact that even comparatively large samples, like complete bodies, can be scanned. These would not fit into a conventional micro-CT scanner.

Abstract-Development of a multi-channel time-to-space terahertz spectrometer

Eva-Maria Stübling, Stefan Busch, Jan C. Balzer, and Martin Koch

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-20-23146

We present a compact sensor head for a multi-channel terahertz (THz) spectroscopy system. A THz pulse generated by a photoconductive antenna is split into spatially separated sub-pulses, which have different transit times. The time-dependent order of the sub-pulses can be translated into a spatial resolution. By using only one pair of antennas the developed sensor head provides up to 20 individual measurement zones with full amplitude and phase information. The sensor head can be integrated into two boxes with a small footprint so that the system is well suited for industrial applications.

© 2016 Optical Society of America

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