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Analysis and Design of Metagratings for Controlling Electromagnetic Waves

Rahmanzadeh, Mahdi | 2023

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 56693 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Khavasi, Amin; Rejaei, Behzad
  7. Abstract:
  8. Metagrating is a new concept for wavefront manipulation that, unlike phase gradient metasurfaces, does not suffer from low efficiency and also has a less complicated fabrication process. However, they have some drawbacks, which we are trying to resolve in this thesis. First, a compound metallic grating is proposed for anomalous reflection. We propose an analytical method for analyzing the electromagnetic response of this grating and show that the structure can have unprecedented near-to-unitary efficiency. Next, two-dimensional (2D) metagratings are proposed for diffraction pattern control. We first present an analytical method for diffraction analysis of 2D compound metallic grating. As a proof of principle, two applications are presented using the proposed analytical method. The first application is a perfect out-of-plane reflector that transfers a normal transverse-magnetic (TM) polarized plane wave to an oblique transverse-electric (TE) polarized plane wave in the $y−z$ plane. The second one is a five-channel beam splitter with an arbitrary power distribution between channels. The performance of the designed metagratings is better than previously reported structures in terms of power efficiency and relative distribution error. In Chapter 5, accurate analytical methods are proposed for diffraction analysis of tunable metagratings consisting of finite numbers of graphene ribbons. In contrast to previous analytical treatments, the proposed method can predict the electromagnetic performance of graphene ribbons not only in the subwavelength regime but also for wavelengths shorter than the array constant. Finally, some applications are designed at the THz regime using the method proposed. We designed these metagratings without requiring even a single optimization in a full-wave solver. In the last section of the thesis, we present accurate and fast methods for the analysis of scattering of electromagnetic waves from an array of time-modulated graphene ribbons. We derive a time-domain integral equation for induced surface currents. Using the method of harmonic balance, this equation is solved for a sinusoidal modulation. The solution of the integral equation is then used to obtain the transmission and reflection coefficients of the time-modulated graphene ribbon array. In contrast with previously reported analysis techniques, our method is extremely fast and can analyze structures with a much higher modulation frequency. Our method also offers a deeper insight into the physical properties of time-modulated graphene ribbons, which may be useful for devising different novel devices. The proposed method paves the path for analytical design of time-modulated graphene-based devices with widespread potential for THz and optical beam-manipulation applications
  9. Keywords:
  10. Subwavelength Apertures ; Analytical Method ; Graphene ; Time-varying Medias ; Metagratings

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