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A Priori Information and Off-Axis Measurements in Terahertz Tomography
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  • Karl Henrik May ,
  • Andreas Keil ,
  • Georg von Freymann ,
  • Fabian Friederich
Karl Henrik May
Fraunhofer Institute for Industrial Mathematics ITWM

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Andreas Keil
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Georg von Freymann
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Fabian Friederich
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Terahertz tomography is a non-contact inspection technique to image objects from multiple angles and reconstruct their 3D volume from intensity and time-of-flight transmission data, without the need for radiation protection measures. Unlike X-rays, terahertz radiation is subject to strong diffraction and refraction as it propagates through dielectric materials, which can deteriorate the image reconstruction quality. Our solution to this problem applies ray tracing, considering the beam shape and an a priori model of the SUT to obtain high-quality image data. We present two reconstruction methods based on the resulting beam path predictions. Method 1 filters out strongly deviated beams, and thus removes the induced artifacts and errors from the reconstruction image. Method 2 employs off-axis measurements, acquiring data along the whole detection plane and this way detecting even strongly deviated beams. Considering these beams and the information they carry in the reconstruction enhances the image quality. Applying these methods to terahertz tomography, even complicated structures can be imaged, provided their feature size is above the diffraction limit. We display the significant enhancements achieved with the two methods by comparing the reconstruction results of different polymeric samples.
2023Published in IEEE Access volume 11 on pages 18311-18325. 10.1109/ACCESS.2023.3243957