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Analysis of EM Wave Propagation in Inhomogeneous Time-Varying Media

Chegnizadeh, Mahdi | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52530 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Memarian, Mohammad; Mehrany, Khashayar
  7. Abstract:
  8. Time-varying media have been in center of attention since recent years for their plethora of applications. Achieving non-reciprocity, one-way propagation, frequency modulation, and signal amplification are some applications of such media which are accessible from microwave to optical frequencies. The aim of this thesis is to first find a method for the analysis of wave propagation in homogeneous time-varying media. To this end, a new formulation is presented based on differential transfer matrices enabling us to find amplitudes, average power, and average energy of a wave in a homogeneous time-varying medium for arbitrary temporal variation of permittivity. In addition,this formulation enables us to analyze a time-periodic medium by extracting Bloch modes and band structures. It is shown that for a modulation frequency of the time-periodic permittivity which is twice the wave frequency, the wave amplitudes will grow significantly. In the second part of the thesis,wave propagation in layered media that each layer has its own time-periodic permittivity (but all have one modulation frequency) is analyzed. To find wave amplitudes in each layer, a formulation based on the transfer matrices is presented, which is applicable for both normal and oblique wave incidence on the layers and is unconditionally stable. To better understand the underlying physics, a method based on Temporal Coupled Mode Theory is presented which is perturbed in time to take into account the behavior of time-varying layers. The most important achievement of this part is that noticeable nonreciprocity in incidence frequency is achievable by using only two quadrature phase time-periodic layers, meaning that the wave will pass the structure in incidence frequency from one side, and approximately no power will pass in incidence frequency from the other side. In this thesis, all calculations made by the formulations are verified using full-wave FDTD simulations or solving the equations numerically
  9. Keywords:
  10. Nonreciprocity ; Transfer Matrix ; Time-varying Medias ; Electromagnetic Waves Propagation ; Inhomogeneous Structure

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