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Industrial applications of THz sensors

Photo by Prof. Martin Koch

Fig. 1: Drying process of a waffle monitored with a THz spectrometer


The interaction of THz waves with matter bases on different physical principles than that of x-rays or visible light. Consequently, sensing with THz waves allows one to „see“ different things. For example, THz waves are strongly absorbed by water. Hence, THz systems can be used to study the water status of plants. They can also be used to monitor industrial drying processes. Fig. 1 shows the drying process of a waffle which was moistened. With progressing time the humidity of the waffle drops and the THz transmission rises.
Besides, there are several other industrial applications which are discussed. This includes:

  • Monitoring polymeric compounding processes
  • Inspection of glued or welded joints between polymer plates
  • Monitoring paper production processes
  • Thickness determination of dielectric films or polymer parts
  • Inspection of pharmaceutical tablets

Literature:

S. Wietzke et al, Terahertz Imaging: A New Non-destructive Technique for the Quality Control of Plastic Weld Joints, Journal of the European Optical Society 2, 07013 (2007) [doi].

C. Jördens and M. Koch, Detection of foreign bodies in chocolate with pulsed THz spectroscopy, Opt. Eng., 47, 037003 (2008) [doi].

N. Krumbholz et al., Monitoring Polymeric Compounding Processes Inline with THz Time-Domain Spectroscopy, Polymer Testing 28, 30 (2009) [doi].

C. Jördens et al, Evaluation of the Leaf Water Status by means of the Permittivity at Terahertz Frequencies, J. Biol. Phys, 35, 255 (2009) [doi].

C. Jördens et al, Terahertz spectroscopy to study the orientation of glass fibers in reinforced plastics, Compos. Sci. Technol. 70, 472 (2010) [doi].

C. Jördens et al, Investigation of the water absorption in polyamide and wood plastic composite by terahertz time-domain spectroscopy, Polymer Testing 29, 209 (2010) [doi].

N. Krumbholz et al, Degree of Dispersion of Polymeric Compounds determined with Terahertz Time-Domain Spectroscopy, Polym. Eng. & Science 51, 109 (2011) [doi].

O. Peters et al, Terahertz spectroscopy for rubber production testing, Polymer Testing 32, 932 (2013) [doi].

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