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Investigation on the Formation of Complex Waves by Guided Modes in Periodic 1D Structures

Ghasemi Nazarlu, Majid | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55938 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Rejaei Salmasi, Behzad; Memarian, Mohammad
  7. Abstract:
  8. Complex waves possess complex propagation constants even in the absence of losses. Such waves may be excited in open- or closed-guided wave structures such as inhomogeneously or anisotropically filled waveguides, coupled right-handed/left-handed transmission lines, and periodic structures. In the absence of losses, complex modes appear in pairs with complex conjugate propagation constants. In open-guided wave configurations, complex modes will be of either the proper or improper (leaky wave) type. Proper complex modes are accompanied by an electromagnetic field that decays exponentially in the transverse direction, away from the waveguide. By contrast, electromagnetic fields associated with improper complex modes increase exponentially away from the waveguide. The propagation constant of complex waves are the poles of the spectral domain Green’s function of the structure. Whether such poles are located on the physical or nonphysical Riemann sheets will determine the proper or improper nature of the modes associated. On the other hand, the spectral domain Green’s function determines the reflection and transmission coefficients of the structure when illuminated by a plane wave. The interesting point is that proper complex waves can play a significant role in the emergence of the extraordinary transmission phenomenon. The main aim of this research is to provide a Green’s function formalism for structures containing a PEC grating that supports extraordinary transmission. It will be shown that the transmission spectrum of this structure is related to the location of the complex pole in the complex plane. In addition, the frequency behavior of these poles using their location in proper and improper Riemann sheets is investigated. It will also be shown that the addition of dielectric slabs over and below the metal grating will change the number and behavior of complex poles, and therefore, significantly affect the transmission spectrum. Finally, the analysis of complex waves will be performed for the metal grating inside a closed metallic waveguide. The results obtained in this thesis have been verified by means of full-wave COMSOL simulations and numerical solution of the equations using MATLAB
  9. Keywords:
  10. Extraordinary Transmission (EOT)Light ; Long Range Interaction ; Green Function ; Complex Waves ; Electromagnetic Fields ; One Dimentional Gratings

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