{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,4]],"date-time":"2026-08-04T16:25:44Z","timestamp":1785860744325,"version":"3.56.0"},"reference-count":23,"publisher":"MDPI AG","issue":"1","license":[{"start":{"date-parts":[[2012,12,20]],"date-time":"2012-12-20T00:00:00Z","timestamp":1355961600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/3.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>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.<\/jats:p>","DOI":"10.3390\/s130100071","type":"journal-article","created":{"date-parts":[[2012,12,20]],"date-time":"2012-12-20T11:27:57Z","timestamp":1356002877000},"page":"71-85","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":65,"title":["Foreign Object Detection by Sub-Terahertz Quasi-Bessel Beam Imaging"],"prefix":"10.3390","volume":"13","author":[{"given":"Gyeongsik","family":"Ok","sequence":"first","affiliation":[{"name":"Food Safety Research Group, Korea Food Research Institute, Backhyun 516, Sungnam, Gyeonggi-do 463-746, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sung-Wook","family":"Choi","sequence":"additional","affiliation":[{"name":"Food Safety Research Group, Korea Food Research Institute, Backhyun 516, Sungnam, Gyeonggi-do 463-746, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kyung","family":"Park","sequence":"additional","affiliation":[{"name":"THz Photonics Creative Research Center, ETRI, Daejeon 305-700, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hyang","family":"Chun","sequence":"additional","affiliation":[{"name":"Food Safety Research Group, Korea Food Research Institute, Backhyun 516, Sungnam, Gyeonggi-do 463-746, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2012,12,20]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"179","DOI":"10.4315\/0362-028X.JFP-11-181","article-title":"Detection of foreign bodies in foods using continuous wave terahertz imaging","volume":"75","author":"Lee","year":"2012","journal-title":"J. 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