Showing papers on "Computational electromagnetics published in 1976"

Transient Electromagnetic Fields

Abstract: Propagation and diffraction of transient fields in non-dispersive and dispersive media.- Integral equation methods for transient scattering.- The singularity expansion method.- Radiation and reception of transients by linear antennas.- A pulsed dipole in the earth.

On the equations governing the electromagnetic perturbations of the Kerr black hole

Abstract: The equations governing the electromagnetic perturbations around a rotating black hole are examined and found to yield a simple, one dimen­sional wave equation with a short range and purely real potential.

The edge condition in electromagnetics

Abstract: The problem of finding the field behavior near a conducting edge in the presence of an arbitrary number of isotropic dielectric wedges is considered Conditions under which finite and infinite fields can exist are derived A principal finding is that for four or more dielectrics it is possible to have finite fields at a knife edge It is shown that the problem is equivalent to finding the fundamental resonance frequency of a resonator formed from a succession of coupled transmission lines

A Perturbation Method for the Analysis of Wave Propagation in Inhomogeneous Dielectric Waveguides with Perturbed Media

Abstract: This paper presents a perturbation method for determining the modes and the propagation constants of TE and TM waves in inhomogeneous dielectric waveguides whose index distributions depart from well-known profiles; e.g., a parabolic profile for which exact solutions can be obtained. Applying the variable-transformation technique to the wave equations, the wave-equation problem is transformed into the related-equation problem. The approximate solutions of the wave equations are obtained solving the related equation. The method is applied to the analysis of lower order mode propagation in a near-parabolic-index medium. The first-order field functions and the second-order propagation constants are given.

An Investigation of the Current Source-Function Technique for Solving Problems of Electromagnetic Scattering

Abstract: The current source-function (CSF) technique is a formulation for electromagnetic scattering problems which does not require the use of vector or scalar potentials. For perfect (electric) conducting scatterers, it yields a Fredholm integral equation of the first kind with a forcing function which is simply proportional to the incident field. Once the solution to the integral equation has been determined, the current or field is found by Green's function techniques. This contrasts with the standard formulations which require that either an integro-differential equation be solved (the Pocklington formulation) or an integral of the incident field be performed (the Hallen formulation). The CSF technique for perfect electric conducting scatterers is based on a direct relationship between the electric field .E and the electric current density Ĵ . For harmonic time dependence e > this direct relationship is V2E + k2E = (VV-J + k2J} = "T— U — — iu>e — — iu)£ — where to is the radian frequency, k is the (free-space) wave number, and e is the permittivity of the medium. The quantity in the braces is the vector current source-function U. Since may not be twice-differentiable in the ordinary sense, U, and IS are interpreted as Schwartz distributions. If IJ is known, then the electric field _E and the current density are easily found. Two classical problems are examined to demonstrate the validity and feasibility of the CSF technique. These are the problems of scattering by a conducting half-plane and by a conducting strip of finite width. First, the half-plane problem is solved analytically by the CSF technique for both Eand H-polarized incident plane waves. For the E-polarization, the CSF technique is almost the same as previous formulations. For the H-polarization, however, a "finite part" integral equation (which can also be interpreted as a convolution equation in distribution theory) must be solved. The resulting current source-function must satisfy a consistency condition, which is developed, in order that it be uniquely determined. Once the current source-function has been found, the current on the halfplane is found by Green's function techniques. The half-plane problem is also solved numerically. In this connection, computer subroutines for evaluating the following special functions are given: x x 1 it cose (1) e HQ (t)dt, t 2 H ^ d D t b d t , H ^ d D t b d t . 0 0 0 -x In addition, a highly accurate subprogram for evaluating an array of Bessel functions of the first kind is given. These computer programs are used in calculating the E-polarization half-plane current by the moment method. Results for a hybrid expansion (with a z 2 function at the edge) are compared with those for an all-pulse expansion. The H-polarization half-plane current is found numerically by the CSF technique by using the moment method results for the E-polarization. For both polarizations, the numerical results show excellent agreement with the analytical solutions. The procedures developed for the half-plane problems appear to be applicable to the strip problem. However, the complete solution of the strip problem by the CSF technique is yet to be discovered. An even

Source theory of molecular electromagnetic interactions

Abstract: Schwinger's theory of sources is examined in connection with the electromagnetic interactions of molecules. Using his constructive principles of causality and space-time uniformity it is shown how to arrive at the starting-points of conventional calculations of photon-molecule scattering and of molecule-molecule interactions through the electromagnetic field.

Analysis of Modes in a Finite-Width Parallel-Plate Waveguide

Abstract: : An efficient method has been developed for analyzing modal characteristics of a finite-width parallel-plate waveguide. The method is based on an extension of Galerkin's procedure applied in the Fourier transform domain. Numerical values of propagation constants and field distributions have been obtained for various structural and modal parameters.

Body of Revolution Modelling and Applications to EMC

Abstract: Many problems in EMC involve structures which are, either exactly or approximately, rotationally sym­ metric. This property can be used to advantage in a method of moments formulation of a problem, In this paper current and potential capabilities of available body of revolution (BOR) computer codes are described and examples are given. Applications of these codes include radiation and scattering from BORs, coupling through apertures in BORs, and mutual coupling between antennas near a BOR. Also these codes are useful for analyzing bodies that only partially satisfy rotational symmetry. An example is a wire arbitrarily located in the vicinity of a BOR. Another example is coupling through arbitrarily shaped apertures in a BOR.

Currents Induced on Conducting Rods by Near and Far Zone Sources

Abstract: Missies in flight are often immersed in an elec­ tromagnetic environment. Whether desirable or not, this EMC situation may cause undue influences on per­ formance of on-board subsystems. To measure these effects, it invariably becomes necessary to experimen­ tally test real-life systems on an antenna range. To cover all threats, large frequency bands as well as high field intensities are needed. Thus the use of near-zone transmitting antennas are often required. The simulation validity of such a test arrangement is a cause for concern, since in flight, the missile experiences plane wave incidence. Are there then significant differences in system response when caused by the near-zone source fields compared to plane wave fields? More importantly, how far away does the source have to be to achieve valid simulation? Since the cost of the test facility depends directly on the power needed, which in turn depend on the separation distance, the answers to these questions are therefore of cri­ tical concern.

Calculation of Microstrip Lines by Means of Singular Integral Equations

Abstract: In case of homogeneous filling the electromagnetic field of the lowest mode in a microstrip line is transverse and can be described by harmonic functions. If the filling is piecewise homogeneous the longitudinal components of electric and magnetic fields arise for lower frequencies being much less than transverse ones. This allows one to use the approximation of transverse electromagnetic waves. The idea of the proposed method is to represent the potential in the form of a Cauchy type integral. Thus the differential equations are satisfied. Then the boundaryr conditions lead to singular integral equations [ I]. We used to solve the equations numerically. In some simplest cases it is possible to get a solution in an analytical form. The main advantages of a method are: I. The method reduces the solution of a two-dimensional problem to one-dimensional one drasticadly shortening computer time. 2. The algorithm of the solution and the form of the equations don't depend on the shape of the line cross section. 3. The conduct of the solution in angular points rigorously corresponds to the static one. 4. From the computational point of view it appeared to be more convenient to apply the method to the line having real geometrical sizes (say finite thickness of a strip). If one considers a line having infinitely thin strips it is convenient to use the representation by Muskhelishvili

Insertion loss due to a spherical shell in low frequency zone

Abstract: Electromagnetic scattering due to a spherical conductor in presence of a slightly conducting dielectric cover has been studied. Numerical results have been presented for a three-layer model, excited by a uniform time harmonic magnetic field, where the intermediate layer accounts for the spacing between the core and the shield. Scattering coefficients for the covered and uncovered situations are compared in terms of an insertion loss parameter. The resulting curves provide information about the interesting frequency bands of supertransmission of energy between the source and the core-conductor. The results may find application in electromagnetic probing of some terrestrial and lunar situations.