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- Type of Document: Ph.D. Dissertation
- Language: Farsi
- Document No: 54444 (05)
- University: Sharif University of Technology
- Department: Electrical Engineering
- Advisor(s): Rejaei, Behzad; Khavasi, Amin
- Abstract:
- In its most general form, analysis of macroscopic electromagnetic behaviour of a medium must include the dependence of magnetic flux density on the electric field and electric flux density on the magnetic filed. This new degree of freedom can lead to new propagation phenomena and result in novel microwave and optical devices. In recent years, numerous theoritical and exprimental studies have been carried out to fabricate these bi-anisotropic materials and understand their behaviour. A particular class of bi-anisotropic materials is electromagnetically equivalent to an anisotropic medium with gyrotropic permittivity and permeability tensors that operate on pseudo-electromagnetic fields. In the first section of this thesis, we show theoretically that unidirectional surface waves can propagate on the surface of homogeneous bi-anisotropic layers with an anti-symmetric chirality tensor. These unidirectional waves pass through an obstacle without backscattering if the obstacle does not cause polarization change. At microwave frequencies, unidirectional propagation may also occur in waveguides containing gyrotropic materials such as ferrites. However, ferrites cannot retain their gyrotropic response at very high frequencies. The use of bianisotropic materials can help to solve this problem. In the second part of this thesis, we analyse a cylindrical waveguide that supports unidirectional modes and consists of two layers of bianisotropic material with anti-symmetric magnetoelectric coupling tensors. We show that the rotationally symmetric modes of the waveguide are unidirectional with transverse pseudo-electric and transverse pseudo-magnetic modes propagating in opposite directions. These modes are surface waves whose electromagnetic field is concentrated near the interface between the two anisotropic materials. They follow the contour of the interface even in the case of sharp discontinuities and pass through an obstacle without backscattering if the obstacle does not change the polarization of the wave. Higher-order modes of the waveguide are also investigated. Although these modes are hybrid modes and not, strictly speaking, unidirectional, they practically behave as the rotationally symmetric mode. Finally, it should be noted that due to limitations of natural materials, bianisotropic materials must be implemented as metamaterials. Extraction of effective parameters of these metamaterials by means of Bloch modes forms the subject of third section of this thesis. Bloch modes and their propagation constants are obtained from eigenvectors and eigenvalues of the generalized transfer matrix of a unit layer of the structure. Effective bulk permittivity, permeability and megneto-electric coupling tensors of the medium are obtained from the dominant Bloch modes. The effect of other Bloch modes are included by means of surface impedance matrices. The scattering parameters of a slab of a bianisotropic metamaterial calculated using effective parameters are in excellent agreement with full-wave electromagnetic simulations
- Keywords:
- Sloshing ; Homogenization ; Unidirectional Surface Wave ; Effective Constitutive Parameters ; Bianisotropic Materials ; Metamaterials Homogenization ; Scattering-Free Waves
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