A Terahertz Holography Imaging System for Concealed Weapon Detection Application
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Many research groups have conducted the investigation into terahertz technology for various applications over the last decade. THz imaging for security screening has been one of the most important applications because of its superior performance of high resolution and not health hazardous. Due to increasing security requirements, it is desirable to devise a high-speed imaging system with high image quality for concealed weapon detection. Therefore, this thesis presents my research into a low-cost and fast THz imaging system for security application. This research has made a number of contributes to THz imaging, such as proposing the beam scanning imaging approach to reduce the scanning time; developing the simulation method of the scanned imaging system; investigating new reconstruction algorithms; studying the optimal spatial sampling criterion; and verifying the beam scanning scheme in experiment. Firstly, the beam scanning scheme is proposed and evaluated in both simulation and experiment, compared to the widely applied raster scanning scheme. A better mechanic rotation structure is developed to reduce the scanning time consumed and realise a more compact system. Then, a rotary Dragonian multi-reflector antenna subsystem, comprising two rotated reflectors is designed to form a similar synthetic aperture being realised in the raster scanned scheme. Thirdly, the simulation of the THz scanning imaging system is achieved by employing Physical Optics algorithm. The transposed convolution and partial inverse convolution reconstruction algorithms are investigated to speed up the image re-construction. Finally, two THz imaging systems based on the raster and beam scanning schemes are assessed and compared in the experiments. The back-propagation, transposed convolution and partial inverse convolution algorithms are applied in these experiments to reconstruct the images. The proposed beam scanning scheme can be further explored together with antenna arrays to provide a compact, fast and low-cost THz imaging system in the future.
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