Terahertz time-domain spectroscopy (THz TDS) holds high potential as a non-destructive, non-contact testing tool. We
have identified a plethora of emerging industrial applications such as quality control of industrial processes and products
in the plastics industry. Polymers are transparent to THz waves while additives show a significantly higher permittivity.
This dielectric contrast allows for detecting the additive concentration and the degree of dispersion. We present a first inline
configuration of a THz TDS spectrometer for monitoring polymeric compounding processes. To evaluate plastic
components, non-destructive testing is strongly recommended. For instance, THz imaging is capable of inspecting plastic
weld joints or revealing the orientation of fiber reinforcements. Water strongly absorbs THz radiation. However, this
sensitivity to water can be employed in order to investigate the moisture absorption in plastics and the water content in
plants. Furthermore, applications in food technology are discussed. Moreover, security scanning applications are
addressed in terms of identifying liquid explosives. We present the vision and first components of a handheld security
scanner. In addition, a new approach for parameter extraction of THz TDS data is presented. All in all, we give an
overview how industry can benefit from THz TDS completing the tool box of non-destructive evaluation.
The worldwide production volume of polymers is still rising exponentially and the number of applications for plastic
components steadily increases. Yet, many branches within the polymer industry are hardly supported by non-destructive
testing techniques. We demonstrate that terahertz (THz) spectroscopy could be the method of choice to ensure high-quality
polymer products. Applications range from the in-line monitoring of extrusion processes and the quality control
of commodities in a mass production up to a total inspection of high-tech safety relevant products. Furthermore, we
present an extension to THz time-domain spectroscopy in the form of a new data extraction algorithm, which derives the
absorption coefficient, the refractive index and the thickness of a sample with very high precision in a single pass.
Apart from that, we discuss the ability of THz systems for quality control of polymeric compounds. Here, it is essential
to monitor the additive content as well as additive inhomogeneities within the mixture. Recently, we built a fiber-coupled
THz spectrometer for in-line monitoring of compounding processes. Additionally, we demonstrate the potential of THz
systems for the non-destructive and contactless testing of structural components. THz imaging is capable of analyzing
material thicknesses, superstructures, the quality of plastic weld joints, and of detecting flaws in components.
Plastics and THz form a very fruitful symbiosis. In return, plastics industry can provide THz systems with custom-tailored
components, which have very attractive properties and extremely low costs. Examples of this development are
photonic crystals or polymeric Bragg filters, which have recently been demonstrated.
Polymers cover the whole range from commodities to high-tech applications. Plastic products have also gained in
importance for construction purposes. This draws the attention to joining techniques like welding. Common evaluation of
the weld quality is mostly mechanical and destructive. Existing non-destructive techniques are mostly not entirely
reliable or economically inefficient. Here, we demonstrate the potential of terahertz time-domain spectroscopy imaging
as a non-destructive testing tool for the inspection of plastic weld joints. High-density polyethylene sheets welded in a
lap joint with varying quality serve as samples for terahertz transmission measurements. Imperfections within the weld
contact area can clearly be detected by displaying the transmitted intensity in a limited frequency range. Contaminations
such as metal or sand are identified since they differ significantly from the polymer in the terahertz image. Furthermore,
this new and promising technique is capable of detecting the boundaries of a weld contact area. Aside from revealing a
contrast between a proper weld joint and no material connection, the size of an air gap between two plastic sheets can be
determined by considering the characteristic frequency-dependent transmission through the structure: The spectral
positions of the maxima and minima allow for the calculation of the air layer thickness.
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