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  1. Dynamic analysis of carbon nanotubes under electrostatic actuation using modified couple stress theory

Analysis of Electromagnetic Effects in Time-varying Bi-Anisotropic Media

Boshgazi, Somayeh | 2025

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 58736 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Mehrany, Khashayar; Memarian, Mohammad
  7. Abstract:
  8. In recent years, the growing research on time-varying linear media has enabled the emergence of novel and versatile wave propagation phenomena that offer significant advantages over conventional static structures. Electromagnetic effects such as non-reciprocity and isolation without the need for magnetic bias field and with optical integration capabilities, frequency conversion without the need for nonlinear elements, and parametric amplification are among the key breakthroughs in this field. These phenomena arise from the interaction of electromagnetic waves with media whose fundamental parameters—namely permittivity, permeability, or electrical conductivity—vary in time. Most existing research have focused on non-reciprocity and have primarily employed time-varying isotropic materials. However, in general, electromagnetic materials can be anisotropic, bianisotropic, chiral, or gyrotropic, offering additional degrees of freedom through tensorial properties of permittivity, permeability, and magnetoelectric coupling, which can be dynamically modulated. Given the limited research on time-varying bianisotropic media, this dissertation investigates electromagnetic phenomena in time-modulated bianisotropic media. To investigate such media, a spatial transfer matrix method based on harmonic balance is developed for periodically time-varying bianisotropic media. Subsequently, for the first time, non-reciprocity in such media is studied in a general framework and starting from the Lorentz reciprocity theorem, suffcient conditions for reciprocity in time-periodic bianisotropic media are derived in terms of the constitutive parameters of the medium. The reciprocity conditions are then examined through examples, such as scattering from a simple slab. Next, we explore the novel concept of inducing chirality and gyrotropy in a non-chiral, non-gyrotropic static medium via temporal modulation of its constitutive parameters. To this end, we introduce a criterion for determining chirality and gyrotropy in time-varying media based on the eigenmodes of the structure. Various types of temporal modulations in anisotropic, non-chiral, non-gyrotropic media are analyzed, and a specific form of modulation that results in gyrotropy is proposed and examined. It is shown that gyrotropy and a type of Faraday effect can be achieved solely through time modulation, without the need for magnetic bias. A practical implementation method for such time-periodic anisotropic media is also proposed, utilizing electro-optic effects. Following that, the concept of achieving chirality through temporal variations in anisotropic time-periodic media is presented. Finally, the concept of stability in time-periodic chiral media is analyzed by investigating the eigenmodes of the system. The findings of this research could lead to the design of novel photonic structures such as optical isolators and polarization rotators without the need for magnetic bias, paving the way for next-generation integrated photonic technologies
  9. Keywords:
  10. Bi-Anisotropic Media ; Time-varying Medias ; Nonreciprocity ; Chirality Problem ; Complex Media ; Gyrotropy ; Space-Time Modulation

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