Showing papers on "Computational electromagnetics published in 1978"
TL;DR: A moment method solution to the problem of radiation or scattering from geometries consisting of open or closed surfaces, wires, and wire/surface junctions is presented in this article.
Abstract: A moment method solution to the problem of radiation or scattering from geometries consisting of open or closed surfaces, wires, and wire/surface junctions is presented. The method is based on the sinusoidal reaction formulation. Several examples of input impedance calculations illustrate the versatility, accuracy, and computational efficiency of the method.
159 citations
TL;DR: In this article, a model is presented which predicts the efficiency of the electromagnetic generation of ultrasonic Rayleigh or Lamb waves in ferromagnetic metal polycrystals, in which two distinct forcing mechanisms are explicitly included, magnetostrictive stresses and Lorentz forces on induced eddy currents.
Abstract: A model is presented which predicts the efficiency of the electromagnetic generation of ultrasonic Rayleigh or Lamb waves in ferromagnetic metal polycrystals. The practically important case in which the static magnetic field, the dynamic magnetic field, and the propagation direction are parallel is considered. Two distinct forcing mechanisms are explicitly included, magnetostrictive stresses, and Lorentz forces on induced eddy currents. The ability of the resulting formulas, which depend only upon the applied magnetic field and independently known elastic and magnetic properties of the material, to correctly predict such important quantities as the field dependence of generation efficiency (both phase and amplitude), the relative importance of magnetic permeability, magnetostrictive coefficients, and electrical resistivity in determining this efficiency, and the decrease in efficiency with distance of the transducer from the sample, is demonstrated by direct comparison to measurements in iron. Results are included in a form useful in predicting the efficiencieosf transducers in new applications.
95 citations
TL;DR: An experimental study of the electromagnetic wave propagation in various tunnels at frequencies between 1 MHz and 1000 MHz is presented in this paper, which provides a better understanding of various propagation mechanisms in underground galleries.
Abstract: An experimental study of the electromagnetic wave propagation in various tunnels at frequencies between 1 MHz and 1000 MHz is presented. The results provide a better understanding of various propagation mechanisms in underground galleries. The analysis shows the existence of a cutoff frequency, and enables one to distinguish three different ranges of frequency characterized by three different modes of propagation. Experimental verification was made in road and mine tunnels of various shapes and sizes. The results show a strong correlation between the propagation characteristics and the transverse dimensions of the tunnel.
58 citations
TL;DR: In this article, a new theory is presented to study the diffraction and absorption of an electromagnetic wave by a two dimensional grating, in order to optimize the geometrical effects of absorbing surfaces.
Abstract: A new theory is presented to study the diffraction and absorption of an electromagnetic wave by a two dimensional grating, in order to optimize the geometrical effects of absorbing surfaces. A computer program is developed, and is verified using various tests.
57 citations
TL;DR: In this article, surface integral representations for electromagnetic wave scattering from dielectric bodies are derived, and the interior resonant solutions, the cause of erroneous solutions, accompanied with the equations presented here and the removal of these solutions are briefly discussed.
Abstract: The surface integral representations are derived for electromagnetic wave scattering from dielectric bodies. Several kinds of integral equations are given for dielectric cylinders immersed in an obliquely incident wave. The interior resonant solutions, the cause of erroneous solutions, accompanied with the equations presented here and the removal of these solutions are briefly discussed.
51 citations
TL;DR: In this paper, the problem of determining the currents excited on a wire enclosed within a rectangular cavity is considered, and an integral equation is formulated for the problem in the frequency domain using equivalent dipole moments to approximate the effects of the aperture.
Abstract: The problem of determining the currents excited on a wire enclosed within a rectangular cavity is considered. The wire and cavity interior are excited by electromagnetic sources exterior to the cavity which couple to the cavity interior through a small aperture in the cavity wall. It is assumed that the wire is thin, straight, and oriented perpendicular to one of the cavity walls. An integral equation is formulated for the problem in the frequency domain using equivalent dipole moments to approximate the effects of the aperture. This integral equation is then solved numerically by the method of moments. The dyadic Green's function for this problem are difficult to compute numerically; consequently, extensive numerical analysis is necessary to render the solution tractable. SampIe numerical results are presented for representative configurations of cavity, wire, and aperture.
23 citations
TL;DR: In this paper, a least square orthogonal polynomial expansion procedure is developed to obtain the average intensity of the pulse as it propagates through the turbulence, which can be used for propagation through random media with discrete scatterers.
Abstract: A new approach is developed to investigate pulse propagation in random media, taking into account the effects of multiple scattering. The technique is based on the idea of temporal moments of the signal. It is shown that these temporal moments are related to the coefficients of expansion for the two-frequency mutual coherence function \Gamma in terms of the frequency separation. These coefficients, and therefore the moments, can be solved analytically in sequence without making assumptions about the strength of the turbulence. Using these moments, a least square orthogonal polynomial expansion procedure is developed to obtain the average intensity of the pulse as it propagates through the turbulence. It is also shown that the technique can be used for propagation through random media with discrete scatterers. An example is given to demonstrate the procedure.
21 citations
01 Jan 1978
19 citations
TL;DR: In this article, an inhomogeneous spherical model of a 3.3 cm radius cranial structure is assumed to be placed symmetically in the near field of a small loop antenna or an electrical dipole antenna at 3 GHz.
Abstract: An inhomogeneous spherical model of a 3.3-cm radius cranial structure is assumed to be placed symmetically in the near field of a small loop antenna or an electrical dipole antenna at 3 GHz. The transitions between the layers are taken to be sharp but sinusoidal. Calculations of the heat potential are performed using a spherical wave expansion technique in which linear differential equations are solved for the unknown multipole coefficients. The results are also compared with the plane-wave excitations. It is seen that a more uniform distribution of the heat potential occurs for the dipole antenna excitation which is also similar to the E-plane distribution in the case of plane-wave excitation. For the loop excitation, a significant hot spot occurs near the center of the structure.
19 citations
TL;DR: In this paper, two new methods, termed "plane-wave correction" and "cylindrical-cell correction", are presented for improving the convergence of moment-method solutions in electromagnetics.
Abstract: Two new methods, termed "plane-wave correction" and "cylindrical-cell correction," are presented for improving the convergence of moment-method solutions in electromagnetics. Convergence is improved because the calculations include an approximation for the variation of the field within each cell.
8 citations
01 Jan 1978
TL;DR: In this paper, an exact method for computing numerically the scattering by an inhomogeneity in a cylindrical waveguide is described, which requires a relatively small amount of computation time and storage capacity.
Abstract: In this paper an exact method is described for computing numerically the scattering by an inhomogeneity in a cylindrical waveguide. The “Generalized Telegraphist's Equations” are used to transform the electromagnetic-field equations into a system of ordinary differential equations. The latter system behaves numerically unstable. A method is given to cope with this difficulty. Numerical results are presented for two- and three-dimensional obstacles in a waveguide of rectangular cross-section and they are compared with those obtained by other methods. Our method requires, in general, a relatively small amount of computation time and storage capacity. Another advantage of the method is its flexibility.
TL;DR: It is shown that the basic Schwarz-Christoffel equation, which at each of the vertices always results in either a pole or a zero, can be accurately and efficiently integrated by employing a combination of quadrature methods and simple variable transformations.
Abstract: Some significant improvements achieved in numerical methods for conformal transformation applicable to electromagnetic field analysis are reported. It is shown that the basic Schwarz-Christoffel equation, which at each of the vertices always results in either a pole or a zero, can be accurately and efficiently integrated by employing a combination of quadrature methods and simple variable transformations. Other transformations are also described to constrain the t -plane constants as required during the direct-search minimization. The complete procedure developed applies to almost any geometry and is found to be computationally faster and more reliable than previous methods. The procedure is illustrated with the aid of an electrical-machine example specifically to which pertain the numerical results and some of the equations.
TL;DR: Time dependent boundary conditions for the boundary values of the electromagnetic fields are obtained for time dependent electromagnetic scattering from bounded material media, and are used to obtain the time dependent integral equation of electromagnetic scattering theory as mentioned in this paper.
TL;DR: In this article, the use of the method of regularisation for solving the ill-posed, in the sense of Hadamard problem, reverse problem of penetration of the time-dependant electromagnetic field into the conducting region was presented.
Abstract: The following paper presents the use of the method of regularisation for solving the ill-posed, in the sense of Hadamard problem, reverse problem of penetration of the time-dependant electromagnetic field into the conducting region. By applying the method of regularisation it was possible to obtain the boundary condition for the electromagnetic field, if the time dependence of the magnetic field intensity in a point of the investigated region is given. By use of a computer, theoretical considerations were illustrated with numerical calculations.
TL;DR: In this article, various sets of conditions are presented which a reasonable theory might be expected to satisfy, in attempting to explain the interaction of the gravitational and electromagnetic fields, and it is shown that each of these sets leads inevitably to the Einstein-Maxwell field equations.
Abstract: Various sets of conditions are presented which a reasonable theory might be expected to satisfy, in attempting to explain the interaction of the gravitational and electromagnetic fields. It is shown that each of these sets leads inevitably to the Einstein—Maxwell field equations. Attention is also drawn to the fact that these equations must be modified if it is furthermore demanded that Maxwell’s equation in flat space—time be an exact solution of them.
01 Jun 1978
TL;DR: In this paper, the problem of reducing such signals to acceptable levels (i.e., hardening) has been studied for hardening systems to the effects of nuclear electromagnetic pulse (EMP) as well as other electromagnetic environments.
Abstract: The mathematical description of the response of a complex system such as an aircraft, a building, etc., to a general electromagnetic stimulus is a problem of exceeding difficulty. High confidence prediction of the signals at the various failure ports (normally pins) is in general beyond the state of the art. Related to the problem of failure-port signal predic tion there is the problem of reducing such signals to acceptable levels (i.e., hardening). This problem has serious implications for hardening systems to the effects of the nuclear electromagnetic pulse (EMP) as well as other electromagnetic environments.
TL;DR: In this paper, a full wave approach is used as the basis for determining the transient electromagnetic field response from nonparallel stratified models of the earth's crust, and analytical expressions are derived for the propagation delays and distortions due to nonuniform ground effects.
Abstract: A full wave approach is used as the basis for determining the transient electromagnetic field response from nonparallel stratified models of the earth's crust. The full wave analysis which satisfies the reciprocity relationships in electromagnetic theory accounts for the scattered radiation fields (considered in Part 1) as well as the scattered surface waves (considered in Part 2). These investigations are relevant to electromagnetic probing in geophysics (active remote sensing) and to problems of communications and navigation using pulsed radio signals. Thus, in this work analytical expressions are derived for the propagation delays and distortions due to nonuniform ground effects. Both analytical and Fast Fourier Transform techniques are used to obtain the solutions.
01 Sep 1978
TL;DR: In this article, the phase anomalies and propagation delays due to irregular ground effects are examined in detail, and the electromagnetic signatures due to transient excitations can reveal the electrical and geometrical characteristics of the earth's surface.
Abstract: The principal motivations for conducting this work are to determine the distortions and delays an electromagnetic pulse undergoes when it propagates across an irregular model of the earth's surface, and to determine whether the electromagnetic signatures due to transient excitations can reveal the electrical and geometrical characteristics of the earth's surface. Thus, in this work, the phase anomalies and the propagation delays and distortions due to irregular ground effects are examined in detail.
TL;DR: In this article, a more refined WKB-type approximation of the solutions, using the method of comparison equations, leads to the result that all guided modes are split with respect to scalar propagation constants.
Abstract: The investigation of electromagnetic waves in two-dimensionally inhomogeneous media leads to an approximation that decouples Maxwell’s equations. The two equations obtained for the longitudinal field components are free from the inconsistencies of the scalar wave approximation. For cylindrically symmetric media the resulting radial equations are basically equivalent to those already derived by Kurtz and Streifer, but a more refined WKB-type approximation of the solutions, using the “method of comparison equations,” leads to the result that all guided modes are split with respect to scalar propagation constants. Calculations carried out for quadratic media indicate that this splitting does not decrease with frequency in the way predicted by previous treatments, using first-order perturbation. The present theory is equally valid for scattered modes, for which an approximate phase shift formula is provided.
02 Oct 1978
TL;DR: In this paper, the ac quasi-static fields produced by electric and magnetic dipole antennas located within a conducting slab have been derived by employing finitely conducting earth-image theory techniques.
Abstract: : Approximate expressions for the ac quasi-static fields produced by electric and magnetic dipole antennas located within a conducting slab have been derived by employing finitely conducting earth-image theory techniques. Asymptotic results have also been obtained by applying the quasi-near approximation to the basic Sommerfeld integrals. The resulting approximations are shown herein to agree closely with previously derived numerical integration results. The resulting expressions are particularly applicable to short range electromagnetic propagation in a shallow sea. (Author)
15 Mar 1978
TL;DR: In this paper, a simple high-frequency approximation for the diffracted field in the forward scattering region is obtained and compared with the exact solution, which is a very simple high frequency approximation.
Abstract: A very simple high-frequency approximation for the diffracted field in the forward scattering region is obtained and compared with the exact solution.
TL;DR: In this article, the electromagnetic fields are treated as systems in which the field equations are the equations of equilibrium, and the subject draws the subject into the unified approach of mechanics, and close analogies to potential and kinetic energy exist and these can be used to provide double bounds to the electromagnetic energy.
Abstract: Electromagnetic fields can be treated as systems in which the field equations are the equations of equilibrium. This formulation draws the subject into the unified approach of mechanics. Close analogies to potential and kinetic energy exist and these can be used to provide double bounds to the electromagnetic energy.
01 May 1978