Enhanced Continuous-Wave Terahertz Imaging with a Horn Antenna for Food Inspection
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Enhanced Continuous-Wave Terahertz Imaging with a Horn Antenna for Food Inspection Geun-Ju Kim & Jung-Il Kim & Seok-Gy Jeon & Jaehong Kim & Kyung-Kook Park & Chang-Hyun Oh
Received: 29 September 2011 / Accepted: 18 April 2012 / Published online: 1 May 2012 # Springer Science+Business Media, LLC 2012
Abstract Continuous-wave (CW) terahertz (THz) imaging with a horn antenna is proposed to enhance the spatial resolution of a THz imaging system. The attached waveguide that is smaller than the wavelength can easily increase the spatial resolution, and the optimized horn flare can significantly increase the transmission power. Consequentially, transmission THz images of a phantom obtained by the amplitude signal using a 0.2 THz wave reveal that the spatial resolution is achieved up to 500 μm. Also, the transmitted power is increased up to 6 times higher compared to the pinhole aperture. The feasibility of CW THz imaging with a horn antenna is demonstrated by the inspection of the organic samples inside food resulting in a relatively high sensitivity for soft organic samples compared with the sensitivity of X-ray imaging to this kind of samples. Keywords Terahertz . Food inspection . Foreign object . Horn antenna . Spatial resolution
1 Introduction Recently, as food safety has become a social issue, the inspection technology is becoming more important. X-ray radiation and ultrasound are commonly used as nondestructive inspection techniques [1–3]. Food inspection using X-ray radiation has benefits such as sterilization and high penetration effects in certain materials. However, in the case of food with active substances such as lactobacillus and fungus, there are concerns of radiation damage and residual radiation in specific materials. Although ultrasound technology is free of radiation hazards, it is not well utilized due to its low resolution and the poor propagation characteristics at boundaries between two types of materials. G.-J. Kim (*) : J.-I. Kim : S.-G. Jeon : J. Kim Advanced Medical Device Research Center, Korea Electrotechnology Research Institute, Ansan 426-170, Korea e-mail: [email protected] K.-K. Park : C.-H. Oh Department of Biomedical Engineering, Korea University, Seoul, Korea
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J Infrared Milli Terahz Waves (2012) 33:657–664
Terahertz (THz) technology has received considerable attention as a nondestructive inspection method because of the properties of THz waves, such as penetration for various materials, low photon energy, and sub-millimeter spatial resolution [4, 5]. Specially, the low photon energy is suitable for food inspection with active substances [6–9]. Although THz waves are useful for food inspection, few studies have been performed because the use of THz waves still has many problems, such as the limited spatial resolution determined by wavelength and the low signal-to-noise ratio. Among them, the limitation of resolution due to wavelength is directly related to the resolution of images and the detectable minimum size of objects. To increase the spatial resolution, researches using a
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