Showing papers in "Electromagnetics in 2007"
TL;DR: In this paper, the authors proposed an accurate central adjoint variable method (CAVM) for estimating objective function sensitivities related to dielectric discontinuities with structured-grid finite difference time domain (FDTD).
Abstract: We propose an accurate central adjoint variable method (CAVM) for estimating objective function sensitivities related to dielectric discontinuities with structured-grid finite difference time domain (FDTD). Our novel approach features accuracy comparable to that of the central finite difference approximation at the response level. Using only two simulations, of the original and the adjoint EM structures, the sensitivities with respect to all the designable parameters are obtained regardless of their number. Our approach uses the same update equations of the conventional FDTD for the adjoint problem which simplifies the implementation. The proposed technique is extended to evaluate the sensitivities of the S-parameters of multi-port electromagnetic structures. Very good agreement is obtained between our approach and the expensive finite difference approximations.
34 citations
TL;DR: Two different measures are introduced in the algorithm for the constraint of the search ranges of the element spacing, and quantized phase excitations are also considered for array feeds with digital devices.
Abstract: This paper proposes an effective approach based on the differential evolution (DE) algorithm for the synthesis of uniform amplitude thinned phased linear arrays. Two different measures are introduced in the algorithm for the constraint of the search ranges of the element spacing, and quantized phase excitations are also considered for array feeds with digital devices. Simulation results of several typical phased array problems are compared with those simulated by the real-coded genetic algorithm (RGA) to demonstrate the effectiveness of the proposed approach.
32 citations
TL;DR: In this article, the authors present a physical way to explain the internal resonance problem for integral equations of scattering, which is a problem that has plagued solutions of scalar and vector integral equations.
Abstract: The internal resonance problem of integral equations is a problem that has plagued solutions of scalar and vector integral equations. A lucid way to explain the occurrence of the internal resonance problem for integral equations of scattering is given in this paper. The physical insight is gotten by performing Gedanken experiments for MFIE for PEC, and for penetrable scatterers when EFIE and MFIE alone are applied. These proofs provide with physical clarity the reasons of the internal resonance problem, as well as the physical character of the internal resonance problem. The connection of the uniqueness of CFIE and the cavity resonance problem is reported.
30 citations
TL;DR: In this article, the static eccentricity fault diagnosis using time stepping finite element (TSFE) method was presented. But the results of applying TSFE method and those obtained by application of winding function (WF) theory are compared.
Abstract: This paper presents the static eccentricity fault diagnosis using time stepping finite element (TSFE) method. In the previous publications on induction motor fault diagnosis by a finite-element method (FEM), steady-state analysis was proposed. White noise, large unbalanced magnetic pull (UMP), and even arc appear during the starting of a faulty induction motor. These phenomena particularly for large induction motor which have longer starting time are very important. In this paper, transient analysis of induction motor under fault is presented. In addition to the static eccentricity fault diagnosis, torque and speed due to the fault are also investigated. In order to show the significant effect of saturation on a faulty induction motor, simulations are carried out for a core with a constant permeability. The results of applying TSFE method and those obtained by application of winding function (WF) theory are compared.
20 citations
TL;DR: In this paper, the authors proposed a hybrid sandwiched magnetic pole design for active magnetic bearings (AMBs), which not only practically reduces the bearing size, but also dramatically diminishes its cost.
Abstract: This paper presents an innovative design for magnetic poles used in active magnetic bearings (AMBs). The proposed hybrid sandwiched magnetic pole design not only practically reduces the bearing size, but also dramatically diminishes its cost. The magnetic force to counterbalance the gravity of the rotor is provided by the embedded permanent magnets (PMs), while the electromagnetic bearing is merely used to regulate the position deviation of the rotor. Therefore, the required electricity consumption to activate the coil wound on the poles is fairly limited. This implies that the required ampere-turns and size of the AMB can both be reduced efficiently. The numbers of associated amplifiers, sensing circuits, and magnetic poles are thus reduced as well. The coupling effect of magnetic forces is taken into account such that either poles for electromagnets (EMs) or the embedded PMs are located 90° apart. The merits of this type of design by orthogonal pole allocation include: simpler control synthesis and deco...
19 citations
TL;DR: In this article, a cylindrical microstrip with radially inhomogeneous substrate (cladding) and an axially infinite metallic patch is examined, and the current on the patch is determined through an integral equation solved by the method of moments.
Abstract: Microstrip structures with a nonplanar shape have been extensively analyzed and studied due to their numerous practical applications. The present work examines a cylindrical microstrip with radially inhomogeneous substrate (cladding) and an axially infinite metallic patch. The permittivity follows a power law inside the cladding, and the Helmholtz equation possesses therein an analytical solution employing Bessel functions of noninteger order. The device is excited by a two-dimensional point source located into the substrate. The current on the patch is determined through an integral equation solved by the method of moments. Different dielectric constants for the cladding and electrical sizes of the microstrip, various positions of the excitation source and angular extents of the patch are considered. Their effects on the operation of the device are shown and discussed.
16 citations
TL;DR: In this paper, the authors describe the computation of the time-domain reflection coefficient for a transient plane wave incident on a planar interface between free space and a Debye medium, where both the TE and TM polarization cases are considered.
Abstract: This report describes the computation of the time-domain reflection coefficient for a transient plane wave incident on a planar interface between free space and a Debye medium. Both the TE and TM polarization cases are considered. The reflection coefficients are written in a simple, compact form and involve a single convolution between exponential and Bessel functions. The use of the expressions in the characterization of Debye materials is explored.
12 citations
TL;DR: In this article, a stochastic collocation method is employed to decouple the collocation nodes, which permits the direct use of a deterministic solver to compute the solution to electromagnetic scattering for each collocation point.
Abstract: This paper presents an efficient approach to quantifying the variation of electromagnetic scattering due to an uncertain geometrical deviation of the scattering surface. This approach employs a stochastic collocation method to decouple the collocation nodes, which permits the direct use of a deterministic solver to compute the solution to electromagnetic scattering for each collocation point. The multidimensional integral introduced by the stochastic collocation method is then evaluated using Stroud's cubatures, which require significantly fewer samples than does the traditional Monte-Carlo method. The accuracy and efficiency of this approach are demonstrated through a few numerical examples, where the results are obtained using the Monte-Carlo method and Stroud's cubatures.
12 citations
TL;DR: In this article, the authors used a time-stepping finite element (TSFE) technique to diagnose the broken rotor bar faults in induction motors using the current spectrum, torque, and speed.
Abstract: In this paper, diagnosis of broken rotor bar faults in induction motors is presented using a time-stepping, finite element (TSFE) technique. Stator current, magnetic flux distribution, magnetic potential vector, magnetic flux density, torque, and speed of the healthy motor and motor with broken rotor bars are calculated. By analyzing the current spectrum, torque, and speed and also by precise analysis of the air gap magnetic field, the occurrence and extent of the broken rotor bars, unbalanced stator current, noise, vibration, and pulsation torque in a faulty induction motor are investigated. In previous publications on the fault diagnosis of induction motors, only one of the above-mentioned signals was used for diagnosis. However, here precise computation and analysis of the field, current, torque, speed, and their relationship and interaction in the analysis and diagnosis of the broken rotor bars are considered.
11 citations
TL;DR: In this article, the authors modified the reflection coefficient of electromagnetic wave incident on the wall of buildings or obstacles that occurs in the mobile communication path by solving the nonlinear Riccati equations.
Abstract: In this paper we modified the reflection coefficient of electromagnetic wave incident on the wall of buildings or obstacles that occurs in the mobile communication path by solving the nonlinear Riccati equations. For this purpose, the building walls are assumed to be inhomogeneous layers of brick and concrete where permittivity changes as a function of the wall thickness. Based on reflection coefficient modification, we proposed a new propagation model using uniform geometrical theory of diffraction (UTD) and geometrical theory of diffraction (GTD) for multiple diffraction paths in cellular mobile radio communication, and calculate the diffraction loss as well as the path loss for a row of buildings with two inhomogeneous faces. The measured reflection coefficient and diffraction loss are then compared to the theoretical results obtained from the proposed model. Our observations reveal good agreement between measurement data and theoretical results. Therefore it can be concluded that the modified...
10 citations
TL;DR: In this paper, the authors considered the scattering of a plane electromagnetic wave by an infinite elliptic metallic cylinder and obtained exact closed form expressions for the expansion coefficients g(2) and g(4) in the relation S(h) = S(0)[1 + g (2)h2+ g (4)h4 + O(h6)] expressing the scattered field and the scattering cross-sections.
Abstract: The scattering of a plane electromagnetic wave by an infinite elliptic metallic cylinder is considered. Two different methods are used for the evaluation. In the first the electromagnetic field is expressed in terms of elliptical-cylindrical wave functions. In the second, a shape perturbation method, the field is expressed in terms of circular-cylindrical wave functions only, while the equation of the elliptical boundary is given in polar coordinates. Analytical expressions are obtained for the scattered electromagnetic field and the various scattering cross-sections, when the solution is specialized to small values of the eccentricity h = c/2a, (h ≪ 1), with c the interfocal distance of the elliptic cylinder and 2a the length of its major axis. In this case exact, closed form expressions are obtained for the expansion coefficients g(2) and g(4) in the relation S(h) = S(0)[1 + g(2)h2 + g(4)h4 + O(h6)] expressing the scattered field and the scattering cross-sections. Both polarizations are considered for n...
TL;DR: In this article, a method for calculating current density in a pair of coaxial conductors whose cross-section has the shape of annulus is proposed, where conductors are connected to a sinusoidal voltage source.
Abstract: A method is proposed for calculating current density in a pair of coaxial conductors whose cross-section has the shape of annulus. The conductors are connected to a sinusoidal voltage source. The method is demonstrated using examples, including the calculation of current density in a cylindrical conductor connected to a sinusoidal voltage source. A similar problem is solved more than 100 years ago, where the wave equation is solved in terms of Bessel functions. This classical solution is analyzed critically.
TL;DR: In this article, an extended version of the third-order strong propertyfluctuation theory (SPFT) is presented, where the component particles are represented as depolarization regions of nonzero volume and convergence of the extended SPFT at the second-order level of approximation is demonstrated within the longwavelength regime.
Abstract: The strong-property-fluctuation theory (SPFT) provides a sophisticated means of estimating the effective constitutive parameters of a homogenized composite material (HCM), which takes account of the statistical distribution of the component particles. We present an extended version of the third-order SPFT in which the component particles are represented as depolarization regions of nonzero volume. Numerical results are provided for a bianisotropic homogenization scenario wherein the HCM is a Faraday chiral medium. Thereby, convergence of the extended SPFT at the second-order level of approximation is demonstrated within the long-wavelength regime.
TL;DR: This work introduces a general antenna array structure and derived its optimal parameters, and then optimized the solution under different quantization errors using a genetic algorithm (GA) and an ant colony optimization (ACO).
Abstract: Antenna arrays are used in the CDMA-based cellular systems in order to increase the systems capacity. Different approaches benefit from the spatial separation between users. Smart and adaptive beam antennas are the best proposed solution for these systems. Several methods are used to provide the system with a radiation pattern that increases the signal-to-interference ratio (C/I). Antenna configuration is the way the array elements are distributed in space. This distribution can influence the design of the beam formation or the adaptation method, such that, the calculation of the different parameters requires a known array configuration. Antenna configuration is discussed in several research papers including planar arrays and circular arrays. Here, we introduce a general antenna array structure and derived its optimal parameters, and then we optimize the solution under different quantization errors using a genetic algorithm (GA) and an ant colony optimization (ACO). Results showed that we can configure th...
TL;DR: A new approach for the pattern synthesis of antenna arrays including mutual coupling effects, based on the combination of the differential evolution algorithm and the complex embedded element patterns, which can be obtained either by measurement or by full wave simulation of the array is introduced.
Abstract: This paper introduces a new approach for the pattern synthesis of antenna arrays including mutual coupling effects, based on the combination of the differential evolution (DE) algorithm and the complex embedded element patterns, which can be obtained either by measurement or by full wave simulation of the array. The proposed approach has the advantage of taking into account many non-ideal effects as compared to other pattern synthesis approaches. Numerical results for the design of a 16-element printed dipole linear array with low sidelobe sum patterns and power patterns are presented to demonstrate the effectiveness of the proposed approach.
TL;DR: In this paper, an efficient optimization algorithm for solving the TE wave imaging problem of a two-dimensional homogeneous dielectric object is investigated and the problem of reconstructing both the shape and the relative permittivity of the cylinder from the measurement of scattered fields is numerically simulated.
Abstract: In this paper, an efficient optimization algorithm for solving the TE wave imaging problem of a two-dimensional homogeneous dielectric object is investigated. The problem of reconstructing both the shape and the relative permittivity of the cylinder from the measurement of scattered fields is numerically simulated. A homogeneous dielectric cylinder of unknown permittivity scatters the incident plane wave whose electric field vector perpendicular to z-axis (TE polarization) in free space and the scattered fields are recorded. Based on the boundary condition and the incident field, a set of nonlinear surface integral equations is derived. The imaging problem is reformulated into an optimization problem and the steady-state genetic algorithm is employed to reconstruct the shape and the dielectric constant of the object. Numerical results show that the permittivity of the cylinders can be successfully reconstructed even when the permittivity is fairly large.
TL;DR: In this paper, the propagation characteristics of circular corrugated waveguides were analyzed using coupled integral equation technique (CIET) and the results for the infinitesimally thin and thick irises were compared with those published in the open literature.
Abstract: The circular corrugated waveguides are useful as slow-wave circuits in traveling-wave tube amplifiers, linear accelerators, and backward-wave oscillators. The study of propagation characteristic of TM waves in circular corrugated waveguides is important for applications such as those above and is the focus of this paper. The propagation characteristics are computed using the coupled integral equation technique (CIET). Both infinitesimally thin irises and thick irises are analyzed. The results for the infinitesimally thin irises are compared with those published in the open literature, where the mode matching technique was used. The results for the thick irises computed using CIET are validated using the three-dimensional electromagnetic (EM) simulators based on finite element method (FEM) and finite integration technique (FIT).
TL;DR: A hybrid technique is presented that combines the finite element and boundary integral methods for simulating electromagnetic scattering from discrete body-of-revolution (DBOR) geometries to provide an efficient tool for the simulation of the scattering by DBOR geometry in electromagnetics.
Abstract: A hybrid technique is presented that combines the finite element and boundary integral methods for simulating electromagnetic scattering from discrete body-of-revolution (DBOR) geometries. The inherent angular periodicity present in a DBOR is utilized to decompose the system matrix into several smaller modal problems, which can be solved efficiently with sparse direct solvers. The proposed method has been validated numerically and provides an efficient tool for the simulation of the scattering by DBOR geometries in electromagnetics.
TL;DR: In this article, the authors proposed a time domain version of the Uniform Asymptotic Physical Optics solution for the field diffracted by a junction formed by two thin layers consisting of highly conducting nonmagnetic dielectrics.
Abstract: The aim of this paper is to propose the time domain version of the Uniform Asymptotic Physical Optics solution for the field diffracted by a junction formed by two thin layers consisting of highly conducting nonmagnetic dielectrics. The incidence direction is assumed to be orthogonal to the junction. The time domain diffracted field is obtained from the knowledge of the corresponding frequency domain expression, which contains the transition function of the Uniform Geometrical Theory of Diffraction, in the hypothesis of resistive sheet having resistivity not depending on the frequency. The Veruttipong's approach is applied by taking advantage from the fact that the corresponding high-frequency solution is given as superposition of the contributions due to each half-plane. The response to an incident unit step function plane wave is considered.
TL;DR: In this paper, a solution for predicting the electromagnetic field diffracted by the edge of a lossy dielectric layer when illuminated by a plane wave at oblique incidence is proposed.
Abstract: This paper proposes a solution for predicting the electromagnetic field diffracted by the edge of a lossy dielectric layer when illuminated by a plane wave at oblique incidence. The starting point is the introduction of electric and magnetic equivalent surface currents in the radiation integral. A physical optics approximation is used for such currents, where results are expressed in terms of the reflection and transmission coefficients of the corresponding infinite structure. A useful approximation and a uniform asymptotic evaluation of the resulting integral allow one to obtain the three-dimensional diffraction coefficients. These are given in terms of the standard transition function of the uniform theory of diffraction. The effectiveness of the proposed technique is assessed via comparisons with FDTD simulations. Due to the peculiarities of this approach, it can be properly extended to the analysis of diffraction phenomena related to a large class of penetrable structures of practical interest.
TL;DR: A program based on an implementation of a genetic algorithm in conjunction with the IE3D simulation software to auto-adjust the geometric parameters of the patch shows distinguished antenna performances while retaining relatively small antenna profile.
Abstract: This paper proposes a dual-band patch antenna design for the applications of wireless local area network (WLAN) and dedicated short-range communications (DSRC). To minimize the antenna size, a shorting plate as well as a shorting pin is used inside the antenna structure. In addition, slots are cut on the patch surface to create dual band operations. In order to accelerate the antenna design procedure and to optimize the antenna performance, we used a program based on an implementation of a genetic algorithm in conjunction with the IE3D simulation software to auto-adjust the geometric parameters of the patch. The program examines the fitness of the design via the antenna's input impedance and bandwidth of operations, and utilizes a natural selection method to generate new values of the parameters. Simulated and measurement results shows distinguished antenna performances while retaining relatively small antenna profile.
TL;DR: In this paper, the authors extended previous works to treat reflector antennas with dielectric surfaces that derive from many practical applications, including the analysis of the scattering from sub-reflectors having frequency selective surfaces in a dual-reflector antenna system.
Abstract: A highly efficient Gaussian beam (GB) method was recently developed to provide a relatively rapid analysis of large, perfectly conducting reflector antennas. This GB method is very efficient because it represents the feed radiation in terms of a set of very few rotationally symmetric GBs and provides an essentially closed form solution for the reflection and diffraction of each GB incidence on the reflector surface. This method completely avoids the time-consuming numerical integrations in the evaluation of radiated fields over the large reflector surfaces that are generally required in conventional approaches of the physical optics and aperture integration techniques. This paper extends previous works to treat reflector antennas with dielectric surfaces that derive from many practical applications, including, for example, the analysis of the scattering from sub-reflectors having frequency selective surfaces in a dual-reflector antenna system. Numerical examples are used to validate this extended GB approach.
TL;DR: The purpose of this paper is to present the implementation of the finite element tearing and interconnecting–Helmholtz (FETI-H) algorithm for the application of large electromagnetic scattering problems formulated via the infinite element method (FEM).
Abstract: The purpose of this paper is to present the implementation of the finite element tearing and interconnecting–Helmholtz (FETI-H) algorithm for the application of large electromagnetic scattering problems formulated via the finite element method (FEM). Details are given to provide maximum performance of this algorithm on a parallel computational platform. Examples show the performance advantages of using this algorithm over the non-preconditioned FETI method and the diagonally preconditioned BiConjugate Gradient Method (BiCGM) solver.
TL;DR: In this article, a variable step length hybrid approach was proposed to solve the differential equations governing the electromagnetic ray path through the ionosphere, which is adaptable to both the gradient of the electron density and the curvature of the path.
Abstract: This paper proposes a variable step length hybrid approach for electromagnetic ray tracing in the ionosphere. The proposed approach adopts a variable step length with discrete intervals, which are adaptable to both the gradient of the electron density of the ionosphere and the curvature of the electromagnetic ray paths. The variable step length approach was then combined with the fourth-order Runge-Kutta (RK) method to solve the differential equations governing the electromagnetic ray path through the ionosphere. Numeric simulation results of several typical scenarios of ionosphere with a parabolic model show obvious improvement in the accuracy of the electromagnetic ray tracing, especially for lower-elevation angles.
TL;DR: A tomographic reconstruction algorithm based on inverse of a set of integral equations relating to Fourier transform of backscattered field data with sought object function at each excitation frequency is presented in this paper.
Abstract: This paper presents a tomographic reconstruction algorithm based on inverse of a set of integral equations relating to Fourier transform of backscattered field data with sought object function at each excitation frequency. Probed structure is a part of a multilayered material half-space containing, in one layer, a cylindrical object of arbitrary cross-section and electrical properties. Both the material and geometrical parameters of the half-space are known. The structure is irradiated by an incident plane wave (TM case). The backscattered field is measured at the probing line over the half-space. As a result, an N×N system of linear equations is derived for each integral equation. A regularized solution for the object function is obtained based on the assumption that the object function is a frequency independent value. This assumption allows coupling of the systems of linear equations at each frequency. We then address experimental results on microwave imaging of different objects for various probed str...
TL;DR: In this paper, a boundary value problem of electrostatic potential penetration into multiple annular apertures in a thick conducting plane is solved rigorously by using the Hankel transform and superposition.
Abstract: This paper examines electrostatic potential penetration into multiple annular apertures in a thick conducting plane. A boundary-value problem of electrostatic potential at thick multiple annular apertures is solved rigorously by using the Hankel transform and superposition. The scattered potentials are represented based on eigenfuction expansion in terms of discrete and continuous modes. The boundary conditions are used to derive a set of simultaneous equations for the discrete modal coefficients. A rapidly convergent series representation for the electric polarizability is presented. The electric polarizability is calculated in terms of aperture geometry to illustrate the behavior of electrostatic potential penetration.
TL;DR: In this paper, a conformal mapping is proposed to transform all of the pertinent boundaries in the potential problem to simple coordinate surfaces in a single cylindrical coordinate frame, and Coupled integral equations for the normal electric current density on each strip are numerically solved using the moment method.
Abstract: The zero-frequency problem of a pair of perfectly-conducting strip electrodes lying on an imperfectly conducting half-space and perturbed by the presence of a nonconductive cylindrical void or tunnel is analyzed. A conformal mapping transforms all of the pertinent boundaries in the potential problem to simple coordinate surfaces in a single cylindrical coordinate frame. Coupled integral equations for the normal electric current density on each strip are numerically solved using the moment method. The effect upon the circuit resistance of various sized subsurface tunnels at arbitrary locations is now easily calculable.
TL;DR: A fast iterative solution based on the quadrature sampled pre-corrected fast fourier transform algorithm used to accelerate a method of moment discretization of the mixed potential integral equation (MPIE) for the analysis of circuits printed in a layered medium.
Abstract: This paper presents a fast iterative solution based on the quadrature sampled pre-corrected fast fourier transform (QSPCFFT) algorithm used to accelerate a method of moment discretization of the mixed potential integral equation (MPIE) for the analysis of circuits printed in a layered medium. The QSPCFFT algorithm is applied to accelerate the computation of all far interactions, and has a complexity that scales as O (N log N) and memory that scales as O(N). The algorithm is efficiently applied to broad-band analysis of printed circuits since the far-field is not constrained by the wavelength, but is determined rather by the local discretization.
TL;DR: In this article, an integral equation for the scattering of an optical field by a spatially varying magnetostatic field in vacuum is presented. And the integral equation can be numerically treated by using the method of moments as well as the coupled dipole method.
Abstract: When a strong magnetostatic field is present, vacuum effectively appears as a linear, uniaxial, dielectric–magnetic medium for small–magnitude optical fields. The availability of the frequency–domain dyadic Green function when the magnetostatic field is spatially uniform facilitates the formulation of an integral equation for the scattering of an optical field by a spatially varying magnetostatic field in vacuum. This integral equation can be numerically treated by using the method of moments as well as the coupled dipole method. Furthermore, the principle underlying the strong–property–fluctuation theory allows the homogenization of a spatially varying magnetostatic field in the context of light scattering.
TL;DR: In this article, an image reconstruction of buried dielectric cylinders coated on a conductor by transverse electric (TE) wave illumination is presented. But the reconstruction is based on the moment method and the unrelated illumination method.
Abstract: This report details image reconstruction of buried dielectric cylinders coated on a conductor by transverse electric (TE) wave illumination. Dielectric cylinders with known cross-section coated on a conductor of unknown permittivities are buried in one half-space and scatter a group of unrelated TE waves incident from another half-space where the scattered field is recorded. Proper arrangement of the various unrelated incident fields avoids the problems of ill-posedness and nonlinearity, and the permittivity distribution can be reconstructed through simple matrix operations. The algorithm is based on the moment method and the unrelated illumination method. Numerical results are given to demonstrate the capability of the inverse algorithm. Good reconstruction is obtained, even in the presence of additive Gaussian random noise in measured data. In addition, the effect of noise on the reconstruction result is also investigated.