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Electromagnetic Devices Based on Virtually Rotating Discontinuities

Seyedrezaei, Zohreh Sadat | 2025

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 58622 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Rejaei Salmasi, Behzad; Memarian, Mohammad
  7. Abstract:
  8. Metasurfaces offer unique capabilities for the unconventional scattering and control of electromagnetic waves. By using metasurfaces, one can arbitrarily manipulate the amplitude, phase, and polarization of incident waves, enabling devices such as flat lenses, holograms, and electromagnetic wave beam deflectors. In recent years, time-varying electromagnetic structures, including time-modulated metasurfaces, have provided enhanced possibilities for controlling electromagnetic waves. By modulating the properties of metasurfaces over time, phenomena such as nonreciprocity, frequency shifts, and parametric amplification can be achieved, which traditionally require magnetic materials or nonlinear effects. In this dissertation, we introduce, analyse, and design metasurfaces with temporal virtual rotation and use this concept for frequency conversion and amplitude enhancement of scattered waves. Additionally, by translating the concept of temporal virtual rotation into transmission line platforms, novel methods for frequency conversion, parametric amplification, and rectification in microwave bands are presented. First, we analytically demonstrate that the scattering of a circularly polarized wave from a metasurface with anisotropic electric susceptibility axes undergoing rotation results in a rotational Doppler effect. Utilizing the rotational Doppler effect, a structure is proposed that fully converts the incident wave to another frequency with amplitude enhancement or attenuation. The results are validated using one-dimensional FDTD numerical simulations. A metasurface configuration is proposed, implemented using a two-dimensional periodic network comprising metallic arms and time-varying capacitors, to realize the required temporal virtual rotation of the electric susceptibility. It is shown that monochromatic or stepwise modulations can lead to the desired rotational Doppler effect. Subsequently, by introducing synthetic circular polarization in transmission lines, the rotational Doppler effect for guided waves is proposed. Using two transmission lines, the vertical and horizontal components of circular polarization are emulated, and by connecting a time-varying capacitive network between the two lines, the rotational Doppler effect is induced for guided waves. Two different approaches for implementing the time-varying capacitive network are presented. Using this circuit, a complete frequency converter and a rectifier are designed and simulated without requiring magnetic materials or nonlinear effects. Furthermore, methods for implementing the proposed ideas and structures in this dissertation using varactors and capacitor bank switching are explored. Finally, a time-varying capacitive block is designed and fabricated on a printed circuit board (PCB), and experimental results for both static and time-varying circuits are compared with simulation results. This research provides a comprehensive framework for advancing the diverse applications of metasurfaces with temporal virtual rotation in communication and electromagnetic systems. It introduces innovative approaches for realizing advanced devices within a time-varying linear system, without the need for magnetic materials or nonlinear effects
  9. Keywords:
  10. Metasurfaces ; Frequency Converter ; Nonreciprocity ; Linear Periodic Time Varying (LPTV)Circuits ; Rotational Doppler Effect ; Microwave Isolators ; Time Varying Metasurfaces

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