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Analysis and Design of Frequency Comb and Frequency Converter using Rotating Time-Periodic Metasurface

Khoshhal, Mohammad | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57467 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Rejaei, Behzad; Memarian, Mohammad
  7. Abstract:
  8. Time-varying electromagnetic structures have provided the possibility of realizing new phenomena and, as a result, new applications, which include non-reciprocity, frequency conversion, amplification, and frequency comb. Among the researches that have been done on time-varying electromagnetic structures, less has been done on the rotating time-varying structure. Rotating time variations have great advantages over other time-varying structures. One of the advantages of rotating time changes is the lack of production of many additional harmonics, which originates from the principle of rotating Doppler shift in frequency. Among its other advantages, it is possible to define a time transformation function to transform a time-varying problem into a static problem, which makes the analysis and design of the structure easier. Recently, a rotating time-varying structure has been investigated, which has the capability of full frequency conversion along with amplification. Using this rotating time variable structure, we have proposed a frequency comb that increases the range of harmonics as the frequency increases and has an amplification form that is a distinguishing feature among the frequency combs that are currently being researched. Also, this frequency comb does not rely on non-linear elements and higher harmonics are produced based on a ladder process. In the next step, taking into account non-ideal conditions such as not being a perfect conductor or not being a perfect mirror, we have improved the frequency comb of the previous stage in terms of efficiency and practical indicators. Also, by adding a filter to this structure, we turn the role of the frequency comb into a broadband frequency converter. This broadband frequency conversion is based on small frequency conversions that occur sequentially and in a ladder, and finally results in a large frequency conversion. Also in the next step, we are looking for a larger power amplification by placing a periodically rotating time-varying structure in place. By analyzing this periodic structure and drawing a dispersion diagram, we observe complex waves in some frequency areas. We will see that in the frequency region where there are complex waves, the bounded power amplification occurs due to the propagation of waves in the periodic structure. In the last step, by using two rotating time varying elements and adjusting the distance and the wave dispersion in the space between them, we examine the issue of non-reciprocity. In this structure, which is very simple, by adjusting the distance of the elements and the wave dispersion, we will achieve a high non-reciprocity of about 0.97. The analysis of these results has been checked and verified by two methods of harmonic balance and time transformation function. The harmonic balance method is a common method of analyzing time-varying structures, which is accompanied by complications. But the time transformation function method, which transforms the time-varying problem into a stationary problem, is an intuitive, simple and flexible method that is very useful in designing structures for specific applications. These results show promising signs of a rotating time-varying structure
  9. Keywords:
  10. Frequency Comb ; Amplification ; Nonreciprocity ; Reinforcement ; Frequency Converter ; Time-Varying Structure

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