Fast Processing Approach for Near-Field Terahertz Imaging with Linear Sparse Periodic Array

10.13039/501100000275-Leverhulme Trust (Grant Number: RL-2019-019)

MIMO Coded Generalized Reduced Dimension Fourier Algorithm for 3-D Microwave Imaging

10.13039/501100000275-Leverhulme Trust under Research Leadership Award (Grant Number: RL-2019-019); 10.13039/501100007914-Brunel University London under Research Development Fund (Grant Number: LBG194); 10.13039/501100007914-2022/2023 Brunel Research Initiative and Enterprise Fund (Grant Number: 12455)

A Terahertz Holography Imaging System for Concealed Weapon Detection Application

PhDMany 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

Study on THz Imaging System for Concealed Threats Detection.

PhD ThesisMany research groups have conducted studies on Terahertz technology for various applications in the last decades. THz imaging for personnel screening is one prospective application due in part to its superior performance compared with imaging microwave bands. Because of the demand for the accurate detection, it is desirable to devise a high-performance THz imaging system for concealed threats detection. Therefore, this thesis presents my research on the low-cost THz imaging system for security detection. The key contributions of this research lie in investigating the linear sparse periodic array (SPA) THz imaging system for concealed threats detection, improving the traditional reconstruction algorithm of Generalized Synthetic Aperture Focusing Technique (GSAFT) to suppress the ghost images and applying the compressive sensing technique into the proposed SPA-THz imaging system to reduce the sampling data but maintain the image quality. The first part of the work is to investigate the linear sparse periodic array (SPA) and its configuration with large element spacing in simulation, deriving the design guideline for such a SPA THz imaging system. Meanwhile, the improved GSAFT reconstruction algorithm and multi-pass interferometric synthetic aperture imaging technique have been proposed to suppress the ghost image and improve the image quality, respectively. Secondly, the compressive sensing technique has been investigated to reduce the sampling data. Therefore, we have proposed the corresponding discrete CS SPA-THz reconstruction model and verified it in simulation. Finally, we have devised a simplified experimental set-up to assess the practical imaging performance, verifying the proposed SPA-THz imaging system. The set-up only uses 1 Tx and 1 Rx scanning on two separate tracks to effectively realize the proposed imaging system. The reconstructed images by the GSAFT and CS approaches with the measured data have both shown good consistency with the simulated results, respectively. And the multi-pass interferometric synthetic aperture imaging has been experimentally proved effective in improving image SNR and contras