Sharif Digital Repository

In this investigation we have taken the viewpoint of the Landau theory for the normal state and have suggested a covariant equation for current density. This suggestion is based on the exact analysis of electrodynamic relations in the intermediate state of superconductors. Our analysis is restricted to the simplest electrodynamic relations. At first we have employed Maxwell's equations with the general Ohm-London equation and have found the general covariant current which takes a covariant form after Lorentz transformation. Finally we have checked it by considering two inertial frames in a simple state  

Recently, a group of novel devices based on conducting interfaces has been proposed. These conducting interfaces can be implemented, for example, by using the inversion layer of MOS structures, trapped charges, or depletion layer charges. It has been shown that these structures can support surface electromagnetic waves. In this paper, the coupling of surface electromagnetic waves supported by conducting interfaces is first analysed. Next, by direct solution of Maxwell's equations and applying appropriate boundary conditions; exact analytical formulation of the dispersion equation has also been derived. Results driven by a coupled mode theory approach are justified by solving the exact... 

In this article, a new general approach has been presented for exact and efficient extraction of eigenpolarizations in anisotropic electromagnetic media with arbitrary constitutive relations. It is shown that the plane wave propagation eigenpolarizations in a linear homogeneous time-independent anisotropic media without free sources, can be obtained through extremizing the difference between stored electric and magnetic energies as a variational functional. It is demonstrated that at these stationary points the wave equation is satisfied by showing that each of the Maxwell curl equations may be obtained by using the other equation as a constraint. Furthermore, it is proven that the theorem... 

A polynomial expansion approach to the extraction of guided and leaky modes in layered structures including dielectric waveguides and periodic stratified media is proposed. To verify the method we compared the results of analysis of a typical test case with those reported in the literature and found good agreement. Polynomial expansion is a nonharmonic expansion and does not involve harmonic functions or intrinsic modes of homogenous layers. This approach has the benefit of leading to algebraic dispersion equations rather than to a transcendental dispersion equation; therefore, it will be easier to use than other methods such as the argument principle method, the reflection pole method, and... 

We present here a simulator that solves the main semiconductor charge and transport equations coupled to Maxwell equations to study receivers based on photoconductive antennas (R-PCAs). Making use of this tool we were able to correctly characterize the operation of these antennas. In doing so, we compared simulations with the results of the semi-empirical expression ITHz(r) ∝σc(t)∗ ETHz(t) employed to evaluate the detected photocurrent by means of the convolution between the photoconductivity in the receiver and the electric field linked to the emitter antenna. We were able to accurately reproduce experimental data with our simulation tool. These kinds of... 

In this study an analytical model based on solving Maxwell equations in the machine layers is presented for linear resolver (LR). Anisotropy, field harmonics, slot effects, number of slots per pole per phase and the effect of tooth skewing are considered in the model. The proposed method is a design oriented technique that can be used for performance prediction and design optimisation of the LR due to its acceptable accuracy and fast computation time. Two- and three-dimensional time stepping finite element method (FEM) is employed to validate the results of the proposed model. Good correlations between the results obtained by the proposed method and the FEM confirm the superiority of the... 

In this paper, a very simple periodic ridge on a symmetric slab waveguide is used for implementing an on-chip CMOS-compatible second-order spatial differentiator. The reflection and transmission coefficients of this structure show that the second derivative is performed in the transmission when the optical beam normally incidents on the periodic ridge. Simulations confirm that the reason behind the second-order spatial differentiation of the incoming beam is the excitation of the guided mode of the periodic ridge. A Maxwell’s equation solver that utilizes the finite element method (FEM) is used to simulate this structure, and an eigenmode solver is utilized for the validation. The results of... 

Three-dimensional vectorial diffraction analysis of gratings is presented based on Legendre polynomial expansion of electromagnetic fields. In contrast to conventional rigorous coupled wave analysis (RCWA) in which the solution is obtained using state variables representation of the coupled wave amplitudes, here the solution of first-order coupled Maxwell's equations is expanded in terms of Legendre polynomials, where Maxwell's equations are analytically projected in the Hilbert space spanned by Legendre polynomials. This approach yields well-behaved algebraic equations for deriving diffraction efficiencies and electromagnetic field profiles without facing the problem of numerical... 

A Legendre polynomial expansion of electromagnetic fields for analysis of layers with an inhomogeneous refractive index profile is reported. The solution of Maxwell's equations subject to boundary conditions is sought in a complete space spanned by Legendre polynomials. Also, the permittivity profile is interpolated by polynomials. Different cases including computation of reflection-transmission coefficients of inhomogeneous layers, band-structure extraction of one-dimensional photonic crystals whose unit-cell refractive index profiles are inhomogeneous, and inhomogeneous planar waveguide analysis are investigated. The presented approach can be used to obtain the transfer matrix of an... 

Free electron lasers have been the subject of intensive interest during the recent decades. In this paper, free electron laser having sheet electron beam with arbitrary inhomogeneous profile of transverse distribution of the beam current density is studied in the linear regime, whereas a novel approach based on the Legendre polynomial expansion of eigenfunctions, already used in analyzing optical structures including stratified structures and diffraction gratings, is adapted to find the eigenfunctions and eigenvalues of the structure. As for this method is unconditionally stable, it works pretty well even in those cases in which the conventional transfer matrix method suffers from numerical... 

In this article, wave propagation characteristics of a size-dependent graphene nanoplatelet (GNP) reinforced composite cylindrical nanoshell coupled with piezoelectric actuator (PIAC) and surrounded with viscoelastic foundation is presented. The effects of small scale are analyzed based on nonlocal strain gradient theory (NSGT) which is an accurate theory employing exact length scale parameter and nonlocal constant. The governing equations of the GNP composite cylindrical nanoshell coupled with PIAC have been evolved using Hamilton’s principle and solved with assistance of the analytical method. For the first time in the current study, wave propagation electrical behavior of a GNP composite... 

In this paper a saturable absorber medium is employed as an optical limiter to reduce the spot size to the range of several tens of nanometres. The characteristics of a Gaussian beam are theoretically analysed upon propagation through the saturable absorber medium. Based on Maxwell equations a system of coupled nonlinear ordinary differential equations for intensity, beam radius and beam curvature is obtained. Theoretical analyses and numerical results show that the behaviour of a Gaussian beam in a saturable absorber medium strongly depends on the initial characteristics of the laser beam. Numerical results indicate that, depending on the initial conditions and a suitable saturable absorber... 

A high-order accurate implicit operator scheme is used to solve steady incompressible slip flow and heat transfer in 2D microchannels. The present methodology considers the solution of the Navier-Stokes equations using the artificial compressibility method with employing the Maxwell and Smoluchowski boundary conditions to model the slip flow and temperature jump on the walls in microchannels. Since the slip and temperature jump boundary conditions contain the derivatives of the velocity and temperature profiles, using the compact method the boundary conditions can be easily and accurately implemented. The computations are performed for a 2D microchannel and a 2D backward facing step in the... 

A novel approach for phototherapy is proposed. The proposed method is based on cell apoptosis according to halting activation of cancer cell membrane receptor by exposure to UV light pulses without any side effect. In the proposed method, gold nanoparticles are directed to cancerous cells by conjugating their surface with specific ligands. UV light is created locally adjacent to cells around the gold nanoparticles. UV light is generated due to nonlinear interaction of visible light with gold nanoparticles because of enhancement in third order nonlinear effects. For example, by using 780 nm laser, 260 nm UV will be generated around the nanoparticle because of third harmonic generation... 

In this study, we simulated and analyzed a plasmonic waveguide modulator based on a single layer of graphene. It includes a graphene sheet, which sandwiches between two layers of silicon dioxide. Then, some gates are arranged on either side of the waveguide on a periodic structure. When an electric field is applied perpendicular to the waveguide plate, the Fermi level of graphene under the gates changes. Detailed analysis is performed by the method of lines based on Maxwell's equations along the propagation direction of the waveguide. Computation of the multi-gate device starts by examining the effect of the Fermi level. The transmission coefficient of the magnetic-field norms of the...