Abstract
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.
Highlights
The detection of foreign objects during the food inspection process is critical to ensuring the quality of food products
Using the non-diffracting nature of Bessel beams, we demonstrate, for the first time to our knowledge, the sub-terahertz imaging of organic foreign objects embedded in food samples
The transmitted quasi-Bessel beam (QBB) imaging shows that its property of extended depth of focus can enable long working distances for food-inspection applications and an efficient spatial resolution
Summary
The detection of foreign objects during the food inspection process is critical to ensuring the quality of food products. Many techniques have been developed commercially and used for the detection and identification of foreign objects during the manufacturing and packaging of food products. X-ray systems can reveal items made of hard nonmetallic materials such as stone, glass, bone, rubber, and plastic when embedded in food products. Unlike X-ray radiation with its ionizing properties, sub-terahertz and terahertz radiation (from 0.1 THz to 10 THz) of low photon energy is nonionizing, making it suitable for investigating biological materials, human-body-related security, and food products [2,3,4]. Terahertz technology can offer a novel quality-inspection method, for food, that offers advantages to conventional noninvasive and nondestructive methods. Terahertz spectroscopic imaging (terahertz time-domain-spectroscopic imaging) and monochromatic imaging (continuous-wave (CW) imaging) have been recognized as promising methods for nondestructive quality inspection in terahertz applications [5,6,7]
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