Sharif Digital Repository

The existing transmission line models of plasmonic nanostructures are modified in this thesis to study the electromagnetic characteristics of nano-plasmonic structures in a more efficeint yet accurate enough fashion. First, rectangular plasmonic cavities made by carving dielectric rectangles within a metallic region are modeled by trasnmission lines of finite length being appropriately terminated at their both ends. The resonance conditon in the proposed model yeilds the resonance frequencies, quality factors, and mode profiles of its correspondig plasmonic resonator. The accuracy of the proposed model is assessed by using the fully numerical finite-difference time-domain method (FDTD)... 

Full numerical methods are usually used for the analysis of periodic structures such as photonic crystals and diffraction gratings. The main drawback of these methods is that they are time-consuming and thus are not appropriate for the design process. In this thesis, approximate and fast methods, based on transmission line models, for the analysis of periodic structures are proposed. To this end, in the first part of the thesis, we investigate one-dimensionally periodic metallic gratings. Longitudinally homogenous metallic gratings, enhanced reflection phenomenon and longitudinally inhomogenous metallic gratings are examined, and simple, and efficient transmission line models for these cases... 

Because of widespread use of optical communication systems, analysis of optical wavepacket behavior during propagation in optical devices is of great importance. On the other hand, constant demand for improving the quality of data transmission and increasing data processing speed raises the necessity of studying novel electromagnetic structures for the purpose of designing new optical devices. Therefore, Photonic Crystal (PC) based structures, for their unique optical properties, have been subject of vast investigation in last two decades. Control of optical wavepacket behavior in photonic crystal based structures is considered in the present dissertation. Depending on the structure under... 

The existing transmission line models of plasmonic nanostructures are modified in this thesis to study the electromagnetic characteristics of nano-plasmonic structures in a more efficeint yet accurate enough fashion. First, rectangular plasmonic cavities made by carving dielectric rectangles within a metallic region are modeled by trasnmission lines of finite length being appropriately terminated at their both ends. The resonance conditon in the proposed model yeilds the resonance frequencies, quality factors, and mode profiles of its correspondig plasmonic resonator. The accuracy of the proposed model is assessed by using the fully numerical finite-difference time-domain method (FDTD)... 

Today as various electronic and telecommunication devices like cell phones and PDAs are being popularized, MMIC technology is gaining a significant importance. One of the priorities of this technology is trying to miniaturize these popular devices. But reducing size of passive microwave components used in these devices requires microwave wavelength to decrease.Components fabricated by conventional deposition techniques aren’t thick enough to reduce the wavelength, so permittivities much higher than those of conventional dielectrics could be a possible solution. Artificial dielectric layers (ADL) can provide such high permittivities.So utilizing these layers can possibly reduce the size of... 

In this dissertation, some computational operators are designed and simulated using plasmonic metastructures. Superiority of graphene over its plasmonics counterparts in terms of exceptional features such as tunability, thinness, and also highly confined graphene plasmons intrigued us to employ graphene-based meta-transmit-array for designing efficient devices in the infrared regime. First off, we propose a transmit-array of metasurfaces containing subwavelength graphene ribbons and evaluate the structure capability in full controlling over amplitude and phase of the impinging wave locally. By considering optics nanocircuits concept, an equivalent admittance is assigned to each metasurface... 

In this thesis we focus on the extraction of resonance modes in photonic crystal resonators. This work could be divided in two different parts: in the first part we apply the Galerkin’s method effectively to the two and three dimensional structures, in the second part that constitutes the main part of this thesis we derive transmission line models for these structures. Fist we derive transmission line models for resonators based on the point defect and line defect in two-dimensional photonic crystals. Then we generalize this model to the three-dimensional photonic crystals. Finally we apply the same approach to the coupled resonators and analyze the coupled resonator optical waveguide. In... 

Power transmission lines, which are responsible for the distribution and transmission of electrical energy from the power plant to the consumer areas, due to their characteristics such as long length and flexibility with low structural damping, face environmental irritations, especially the galloping phenomenon, causing many damages annually. In this study, it has been attempted to reduce the vibrations of power transmission lines by designing a robust active control and by using intermediate actuators in such a way that the failures of these lines can be prevented. For this purpose, linear modeling of the system and designing the controller using the pole replacement method have been done....