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Design and Optimization of a Lens for Beam Shaping in a Terahertz Standoff Imaging System

Abbaszadeh, Afshin | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51589 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Ahmadi Boroujeni, Mehdi
  7. Abstract:
  8. Terahertz waves have three important features that make them suitable for security imaging. 1. THz waves can penetrate or can be absorbed from many of non-metallic and non-polar materials and are perfectly reflected from most of the metals, 2. Drugs and explosives have terahertz spectra that can be detected by THz imaging, 3. THz waves do not have an ionizing effect and are harmless to the human body. Lenses can be considered as a major component of the terahertz imaging systems. Because of the relatively large terahertz wavelengths compared with wavelengths, compression, and decreasing the dimensions of the lenses in these systems matters a lot. In addition, reducing the wave reflection from the lens surface and achieving the desired shaped beam in the lens output are another of their design goals. To realize a flat lens in the terahertz regime, one can use metamaterials (meta-surfaces), plasmonic and quasi-plasmonic structures, photonic crystals, and other structures based on dielectric materials. In this project, the design, simulation and fabrication process of flat lenses in the THz frequency range are proposed that shape Gaussian beam and transform it into a beam with a uniform and flat energy distribution that enhance the efficiency of illumination setup in THz standoff security imaging systems. To this end, we described THz standoff security imaging system and the importance of beam forming in these systems. We also introduce two methods for beam forming: 1. Optical map transform and 2. Gerchberg-saxton algorithm. We introduced and simulated several metasurfaces for manipulating of input beam and presented design process and simulation of all dielectric metasurface based beam shapers and the design, simulation, and fabrication process of refractive-based beam shapers. We also verified the results by analytical method, ray tracing method and equivalent refractive index model of the lens
  9. Keywords:
  10. Terahertz Imaging ; Flat Lens ; Metamaterial ; Beam Shaping ; Stand-Off ; Terahertz Technology

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