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Sensors 2013, 13(1), 71-85; doi:10.3390/s130100071

Foreign Object Detection by Sub-Terahertz Quasi-Bessel Beam Imaging

1 Food Safety Research Group, Korea Food Research Institute, Backhyun 516, Sungnam, Gyeonggi-do 463-746, Korea 2 THz Photonics Creative Research Center, ETRI, Daejeon 305-700, Korea
* Author to whom correspondence should be addressed.
Received: 23 October 2012 / Revised: 4 December 2012 / Accepted: 11 December 2012 / Published: 20 December 2012
(This article belongs to the Section Physical Sensors)
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Food quality monitoring, particularly foreign object detection, has recently become a critical issue for the food industry. In contrast to X-ray imaging, terahertz imaging can provide a safe and ionizing-radiation-free nondestructive inspection method for foreign object sensing. In this work, a quasi-Bessel beam (QBB) known to be nondiffracting was generated by a conical dielectric lens to detect foreign objects in food samples. Using numerical evaluation via the finite-difference time-domain (FDTD) method, the beam profiles of a QBB were evaluated and compared with the results obtained via analytical calculation and experimental characterization (knife edge method, point scanning method). The FDTD method enables a more precise estimation of the beam profile. Foreign objects in food samples, namely crickets, were then detected with the QBB, which had a deep focus and a high spatial resolution at 210 GHz. Transmitted images using a Gaussian beam obtained with a conventional lens were compared in the sub-terahertz frequency experimentally with those using a QBB generated using an axicon.
Keywords: terahertz imaging; sub-terahertz imaging; quasi-Bessel beam; axicon; foreign object detection; FDTD terahertz imaging; sub-terahertz imaging; quasi-Bessel beam; axicon; foreign object detection; FDTD
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Ok, G.; Choi, S.-W.; Park, K.H.; Chun, H.S. Foreign Object Detection by Sub-Terahertz Quasi-Bessel Beam Imaging. Sensors 2013, 13, 71-85.

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