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    Analysis of Nonlinear Effects in Microstrip High Temperature Superconductor (HTS) by FDTD Method

    , M.Sc. Thesis Sharif University of Technology Mollai, Sajjad (Author) ; Shishegar, Amirahmad (Supervisor) ; Fardmanesh, Mehdi (Supervisor) ; Banai, Ali (Supervisor)
    Nowadays high temperature superconductors (HTS) are very efficient and useful materials for microwave devices such as planar filters, resonators, hybrids, antennas and delay lines. The advantages of these devices are high quality factor, low insertion loss and reduced size. However the nonlinear effects of superconductors in high incident powers has limited usage of HTS in some applications and causes disadvantages such as reducing quality factor, intermodulation distortion and third harmonic generation of signal. The nonlinear effects of superconductor are due to the dependency of penetration depth and normal conducting coefficient to the current density of superconductor. Nonlinr effect... 

    Numerical Simulation, Tunability and Experimental Investigation of Random Lasers and Using ZnO Nanosheets in these Lasers and UV Photodetectors

    , Ph.D. Dissertation Sharif University of Technology Ghasempour Ardakani, Abbas (Author) ; Mahdavi, Mohammad (Supervisor) ; Bahrampour, Ali Reza (Supervisor) ; Taghavinia, Nima (Co-Advisor)
    In this thesis, first, random lasing in a three dimensional disordered medium has been simulated using FDTD method and some properties of random lasers which were observed by others in the previous experiments have theoretically been shown. Our simulation results show that when the density of particles increases to an upper limit, the intensity of lasing modes is enhanced. Also, the effects of pumping rate and particle size on the number of lasing modes and their intensity are studied. Lasing threshold of laser modes in different disordered systems is calculated and it is shown that by an appropriate selection of the central frequency of gain line-shape, the output power intensity of random... 

    Design of Plasmonic Systems for Nanobiophotonic Applications

    , Ph.D. Dissertation Sharif University of Technology Shahmansouri, Afsaneh (Author) ; Rashidian, Bizhan (Supervisor) ; Vosoughi, Manouchehr (Supervisor) ; Shahrokhian, Saeed (Co-Advisor)
    In this thesis periodic plasmonic nanostructures are studied for detection of biological specious. The behavior of metal nanostructure arrays under normal incidence has been widely reported. However, simulation of periodic dispersive structures under oblique incidence requires newer formulations. Formulations, and algorithms based on modified split-field finite-difference time-domain (SF-FDTD) method are introduced, permitting analysis of metallic nanostructures arrays under oblique incidence. These novel algorithms are practically implemented on a parallel processing system based on graphics processing unit (GPU). Test and verification of these formulations are done by analyzing referenced... 

    Analysis of Nonlinear and Plasmonic Nano-Photonic Structures

    , M.Sc. Thesis Sharif University of Technology Naqavi, Ali (Author) ; Mehrany, Khashayar (Supervisor) ; Khorasani, Sina (Supervisor)
    Different methods of shifting and shaping of space-time electromagnetic pulses are in this work investigated by nonlinearity and/or dispersion. Developing two dimensional (2D) finite difference time domain (FDTD) codes in the nonlinear regime and taking the optical dispersion of ideal metals into account, nanophotonic and plasmonic structures are analyzed in this thesis.
    Goos-Hänchen shift, superprism effect, and optical bistability are particularly emphasized. A heuristic approximation is presented to extract the Goos-Hänchen shift at the interface of 1D and 2D photonic crystals. The superprism effect for electric polarization – where the electric field vector is perpendicular to the 2D... 

    Extension of unified formulation for the FDTD simulation of nonlinear dispersive media

    , Article IEEE Photonics Technology Letters ; Volume 22, Issue 16 , 2010 , Pages 1214-1216 ; 10411135 (ISSN) Naqavi, A ; Miri, M ; Mehrany, K ; Khorasani, S ; Sharif University of Technology
    A simple approach is extended for the simulation of Kerr-nonlinear and/or dispersive media through the finite-difference time-domain method. The scheme is able to include different types of linear and nonlinear dispersion in a single and unified formulation. It also provides a method for the simulation of nonlinear dispersive media in such a way that saving time is possible. Also, a new simple technique is presented for the implementation of sources having arbitrary profiles and arbitrary radiation angles. The technique is particularly suited for easy modeling of unidirectional sources like Gaussian beams  

    Improvement and Expansion of Characteristic Green’s Function-Complex Images Method for Extraction of Green’s Function of Finite Dielectric Structures

    , Ph.D. Dissertation Sharif University of Technology Torabi, Abdorreza (Author) ; Shishegar, Amir Ahmad (Supervisor) ; Faraji-Dana, Reza (Co-Advisor)
    Finite dielctric structures are commonly used in optical devices, Microwave Integrated Circuitc (MICs) and printed antennas. To analyze these structures, full-wave analysis methods cannot be employed easily. They need huge computer resources and are time-consuming especially for electrically large structures. On the other hand, asymptotic techniques may not be exact enough for these structures. In this thesis, MPIE technique is chosen as an accurate and efficient technique for analyzing these structres. To use this technique, the magnetic vector potential and electric scalar potential are required. Uniform and closed-form spatial Green's function for finite dielectric structures is... 

    Fabrication and Characterization of Transparent and Flexible Conductive Layers Based on Copper Nanofibers

    , Ph.D. Dissertation Sharif University of Technology Nikzad Alhosseini, Mohammad Javad (Author) ; Sadrnezhad, Khatiboleslam (Supervisor) ; Mahdavi, Mohammad (Supervisor)
    The Transparent electrode (transparent conductive layer) is an essential component of electro-optical devices, especially screens, solar cells and touch screens. Today, most semiconductor oxides such as ITO are used for this purpose, which have problems such as inflexibility, high cost, environmental degradation and ion penetration in organic displays. In this research, the design, simulation and fabrication of a transparent electrode with a network of metal nanowires with low resistance between cross fibers and high aspect ratio during the production stages of polymer mold, metal coating and characterization has been done. Using the reducing atmosphere in the sputtering chamber, the... 

    Multi-conductor transmission line networks in analysis of side-coupled metal-insulator-metal plasmonic structures

    , Article Optics Communications ; Vol. 313, issue , 2014 , pp. 375-381 ; ISSN: 00304018 Eshaghian, A ; Bahadori, M ; Rezaei, M ; Khavasi, A ; Hodaei, H ; Mehrany, K ; Sharif University of Technology
    An approximate and accurate enough multi-conductor transmission line model is developed for analysis of side-coupled metal-insulator-metal (MIM) waveguides. MIM waveguides have been already modeled by single conductor transmission lines. Here, the side coupling effects that exist between neighboring plasmonic structures are taken into account by finding appropriate values for distributed mutual inductance and mutual capacitance between every two neighboring conductors in the conventional single-conductor transmission line models. In this manner, multi-conductor transmission line models are introduced. Closed-form expressions are given for the transmission and reflection of miscellaneous MIM... 

    Implementation of open boundary problems in photo-conductive antennas by using convolutional perfectly matched layers

    , Article IEEE Transactions on Antennas and Propagation ; Volume 64, Issue 11 , 2016 , Pages 4919-4922 ; 0018926X (ISSN) Moreno, E ; Hemmat, Z ; Roldan, J. B ; Pantoja, M. F ; Bretones, A. R ; Garcia, S. G ; Faez, R ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    A method to simulate an open boundary problem within the finite difference time domain approach for the emission of photo-conductive antennas is presented here. For this purpose, we use convolutional perfectly matched layers (CPMLs). In these devices, the semiconductor region, where transient currents are present in simulation time, is considered to be an 'active' medium. This medium is extended virtually beyond its boundaries or the computational domain limits. We explain in this communication how to simulate the transient state of a semiconductor in a CPML region as well as the potential of the method developed to solve conventional practical applications  

    Computational electromagnetics in plasmonic nanostructures

    , Article Journal of Materials Chemistry C ; Volume 9, Issue 31 , 2021 , Pages 9791-9819 ; 20507534 (ISSN) Amirjani, A ; Sadrnezhaad, K ; Sharif University of Technology
    Royal Society of Chemistry  2021
    Plasmonic nanostructures have emerging applications in solar cells, photodynamic therapies, surface-enhanced Raman scattering detection, and photocatalysis due to the excitation of localized surface plasmons. The exciting electric field resulting from the collective oscillation of free electrons is highly dependent on the dielectric medium, shape, size, composition, and configuration of plasmonic nanostructures. From an engineering perspective, one can tune the optimal properties in the desired applications of geometrical parameters such as the shape, size, and nanoparticles' configuration. Such optimization should be performed analytically (with exact solutions) or numerically (with... 

    Radio-wave Propagation Modeling Using Statistical Models and Ray Tracing for Wide-band Wireless Telecommunications

    , Ph.D. Dissertation Sharif University of Technology Atamanesh, Mehran (Author) ; Farzaneh, Forouhar (Supervisor) ; Shishegar, Amir Ahmad (Co-Advisor)
    Ever-increaing demand for wireless communication systems impels an efficient system planning before the system deployment. The very first step of the planning is radio-wave channel modeling. Generally, all propagation models can be categorized in three types of models: Emprical models, semi-emprical models and deterministic models. The statistical and semi-emprical models can give a quite prompt signal level prediction over the vast propagation area using few computations. In the recent wireless services which wider bandwidth is required, only the signal level prediction cannot give a proper perspective of design and planning. The parameters such as the power-delay profile, rms delay spread;... 

    FDTD analysis of distributed amplifiers based on the fully distributed model

    , Article 2007 Asia-Pacific Conference on Applied Electromagnetics, APACE2007, Melaka, 4 December 2007 through 6 December 2007 ; 2007 ; 1424414350 (ISBN); 9781424414352 (ISBN) Mirzavand, R ; Abdipour, A ; Shishegar, A. A ; Sharif University of Technology
    In this paper a wave approach has been introduced to study the performance of a distributed amplifier. The time domain response of a FET is obtained by means of the fully distributed model. By applying the procedure to a pi-gate GaAs MESFET, the S matrix is computed from time domain results over a frequency range of 2-20 GHz. Scattering parameters of gate and drain lines are extracted from three-dimensional FDTD simulation. The result obtained by this wave approach is compared with device lumped model and Quasi static approach of transmission line. © 2007 IEEE