Modeling, Design and Efficient Low-Cost Digital Implementation of Millimeter-Wave Imaging System

Shayei, Ali | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52515 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Shabany, Mahdi; Kavehvash, Zahra
  7. Abstract:
  8. Recently, there has been an increasing trend towards the use of millimeter-wave (MMW) imaging in various detection applications. This is mainly due to two factors: first, the radiation in the MMW band (30–300 GHz) is nonionizing and safe to use and second, it is able to penetrate through most dielectric materials as well as poor weather conditions, such as smoke and fog. With these potentials, MMW imaging has been used in a variety of applications, including target surveillance and precision target imaging, safe aircraft landing, highway traffic monitoring in fog, remote sensing for civil applications and concealed threat object detection for security concerns. Moreover, it can also find applications in nondestructive testing fields where the dielectric material defects are detected with the good penetration ability of MMW signals. Among MMW imaging practices, the detection of threatening objects concealed under clothing, called concealed weapon detection (CWD), has been one of the most studied applications. A resolution-improved active millimeter-wave (MMW) imaging structure, based on the theory of structured illumination, is proposed in this thesis. The structured illumination is a well-defined concept for surpassing the diffraction limit in optical microscopy. This idea has not yet been employed for MMW image resolution improvement due to practical limitations in producing the desired grating patterns. Therefore, a desired fringe pattern is produced here and tailored for a MMW imaging system through antenna array synthesis. In the proposed scheme, the structured illumination has been implemented for improving the MMW image resolution. Furthermore, an adaptive approach has been proposed in order to generalize the structure for resolution improvement in all required directions in a very fast manner. Electromagnetic simulation results show at most twofold improvement in the image resolution through the proposed MMW imaging structure. In addition, a new approach toward material detection and classification, based on the spectral analysis of millimeter-wave images, using machine learning technique is proposed. The focus of this technique to detect concealed dangerous materials. It is shown that by using adequate number of training data captured from different materials of interest, the trained machine could detect concealed dangerous materials with an acceptable accuracy. The training phase is performed with materials of varying thickness, shape, background, covering layers and distance. The training data is collected with laboratory experiments in the frequency range of 27-31 GHz with 51 frequency samples. The results show more than 92 percent accuracy in differentiating various materials based on the true-alarm-rate (TAR) metric. A calibration technique and an FFT based reconstruction method is also proposed, which improves the reconstruction speed without degrading the quality
  9. Keywords:
  10. Imaging ; Image Reconstruction ; Image Processing ; Millimeter Wave ; Millimeter-Wave Imaging ; Security Screening ; Digital Implementation

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