Showing papers on "Computational electromagnetics published in 1982"

Accuarte Modelling of Frequency-Dependent Transmission Lines in Electromagnetic Transient Simulations

Abstract: The parameters of transmission lines with ground return are highly dependent on the frequency. Accurate modelling of this frequency dependence over the entire frequency range of the signals is of essential importance for the correct simulation of electromagnetic transient conditions. Closed mathematical solutions of the frequency-dependent line equations in the time domain are very difficult. Numerical approximation techniques are thus required for practical solutions. The oscillatory nature of the problem, however, makes ordinary numerical techniques very susceptible to instability and to accuracy errors. The, methods presented in this paper are aimed to overcome these numerical difficulties.

Universal Machine Modeling for the Representation of Rotating Electric Machinery in an Electromagnetic Transients Program

Abstract: This paper describes the theory, development and practical application of a new universal machine module, which can be used for the transient analysis of motor/generator phenomena in large and complex power networks. In the general case, doubly-fed electric machines with an arbitrary number of coils and magnetic saturation can be represented. Included are all of the major classes which are of common industrial interest: synchronous and induction machines of 1, 2, or 3 phases, and dc machines. A procedure for maximizing the flexibility of the machine-network interface is explained. Computer implementation has been variably- dimensioned, so that any number of motors or generators can be interconnected with mechanical systems and electric networks of arbitrary size and configuration. Universal machine modeling is now a standard feature of the BPA Electromagnetic Transients Program (EMTP), which is widely used on numerous different computers.

Optimization techniques and inverse problems: Reconstruction of conductivity profiles in the time domain

Abstract: The iterative probing of an inhomogeneous lossy dielectric slab, whose conductivity is unknown, is discussed. The probing is done in the time domain from the measurements of the field on the interface when this slab is illuminated by a known field. An exact integral formulation is used. Minimization of a cost function, characteristic of the discrepancy between the measured field and the field which would be scattered by a known slab, is specified by the optimization theory. The notion of the adjoint state of the field is introduced. The influence of some parameters of this minimization is studied. Great importance is given to the sensitivity of the probing as function of the amplitude of errors in the data. Such an iterative probing appears fast, accurate, and efficient, even in the case of large errors.

The scattering of electromagnetic waves by single hydrometeors

Abstract: This paper is concerned with the state of the art in the calculation of electromagnetic wave scattering by hydrometeors. Four methods currently being used are briefly described (point-matching, T matrix, unimoment, and Fredholm integral equation), and aspects of their computational implementation are reviewed and compared. The ranges of validity of three types of approximation are discussed—those with respect to size, orientation, and frequency. Finally, scattering patterns from various sizes of spheroidal raindrop at 11.7 GHz are briefly discussed.

A simple technique for solving E -field integral equations for conducting bodies at internal resonances

Abstract: A simple but effective method is presented to analyze electromagnetic radiation and scattering from condueting bodies at frequencies corresponding to internal resonances of a cavity of the same shape. The advantage of this technique is that it requires only the E -field integral equation and hot both E -field and H -field as required by the combined fields formulation. It is shown theoretically that this method produces a solution with minimum norm and converges monotonically as the order of the approximation is increased. The minimum norm solution for the current density given by the E -field integral equation is not the correct current density as there is a portion of the resonant current that exists on the body. However, the minimum norm solution indeed provides the true scattering fields. This technique may also be utilized for obtaining a minimum norm solution for nearly singular and singular matrix equations. Examples are presented to illustrate the application of this technique.

The effects on pair correlation function of coherent wave attenuation in discrete random media

Abstract: The Percus-Yevick approximation (P-YA) of pair correlation function for hard spheres is combined with the T -matrix formulation to study the coherent wave attenuation of electromagnetic wave propagation in a discrete random medium. The effect of the pair correlation function is seen to be significant at high fractional volumes of the discrete scatterers ( \geq0.125 ), but also depends on the frequency of the propagating wave-the effect being less at higher frequencies. The results are compared with previous calculations which employed the "well-stirred approximation" (WSA) for the pair correlation.

Unified theory of near-field analysis and measurement: Nonmathematical discussion

Abstract: A new unified theory of near-field analysis and measurement emphasizes highly accurate, extremely efficient data processing to yield, e.g., radiation, receiving, and scattering patterns, and absolute gain values. The theory includes 17 types of plane rectangular and plane radial scanning, a more accurate and efficient plane polar scanning, spherical scanning, various types of circular cylindrical scanning, many procedures for determining complex dyadic scattering patterns, the extrapolation method for gain and effective area, and application of symmetry analysis to scattering and inverse scattering analysis. High accuracy is obtained by expressing the fields as linear combination of exact solutions of the differential equations involved (Maxwell's in the electromagnetic (EM) cases) and by using exact expressions for their transformations under coordinate changes. High efficiency is obtained with natural orthogonalities of both the solutions and transformation coefficients with respect to integration, especially summation, and implemented with the fast Fourier transform (FFT) as an approximation-free symmetry decomposition. The unified theory is based upon relativistic and gauge invariances, symmetry analysis, and the scattering matrix theory; it yields all the preceding facets and systems, both electromagnetic and scalar, and the single unified notation, general equations, and explicit expressions for the quantities which vary with the physical or scanning system. A nonmathematical discussion of other papers on the theory is provided. Many of the conceptual errors of the literature are corrected. The advantages and limitations of near-field measurements are described, and scanning systems are compared.

Electromagnetic Wave Theory and Remote Sensing

Abstract: Electromagnetic waves are studied with applications to microstrip antennas, 1'2 geophysical subsurface probing,3' 4 scattering from helical structures5 '6 and Smith-Purcell radiation from metallic gratings.7 Radiation and resonance characteristics of two coupled circular microstrip disk antennas are studied rigorously using numerical techniques, matched asymptotic analysis, and the newly developed Hankel transform analysis.1,2 The electromagnetic fields due to dipole antennas in a two--layer dissipative medium is solved using the quasistatic approximation. 3 The solutions in integral forms are calculated with brute force numerical integration methods, the multi-image approach with the steepest descent method, the normal mode approach with the residue method, and a hybrid approach with combinations of the above methods. Electromagnetic wave scattering from helical structures has been studied using the physical optics and modal approaches. The fields scattered by a thin wire helix of finite extent is investigated using physical optics and the geometrical theory of diffraction.5 The geometrical theory of diffraction result is obtained as a high frequency limit of the physical optics approximation by applying the saddle point technique to the integral representation of the physical optics field. The electromagnetic wave scattering by a tape helix of infinite extent is studied by using Floquet wave expansion for its guided modes and scattered fields.6 The Smith-Purcell radiation problem is solved taking into account the penetrable properties of metallic gratings.7 When an electron beam streams across the surface of a metallic grating, emission of electromagnetic radiation occurs. It is shown that maximum radiation occurs when the surface plasmon mode is excited.

An integral-equation/singularity-method approach for 3-D electromagnetic field determination in the end region of a turbine-generator

Abstract: A mathematical model using an integral-equation/singularity-method approach is derived for determining the magnetic field and electromagnetic forces induced by current-carrying conductors in a region bounded by 3-D material-body surfaces which have complex configurations. Special analytical and numerical techniques that eliminate near-field computational difficulties and bypass the cumbersome matrix manipulations required by other integral-equation approaches are described. A comprehensive computer program package has been developed using this approach for obtaining the 3-D solutions in the end region of a turbine-generator due to armature end windings. Special computational techniques for handling the complex end-winding and surface geometry are described and detailed numerical results are presented for the 3-D field solution and the forces acting on the conductors.

Scattering of plane electromagnetic waves by a grating of conducting cylinders embedded in a dielectric slab over a ground plane

Abstract: The problem of scattering of electromagnetic waves by periodic conducting cylinders embedded in a dielectric slab backed by a plane reflector has been of great interest. A numerical integral equation technique is presented for the analysis of this problem. The solution of the integral equation yields the induced surface currents on the cylinders from which the powers in various reflected modes are calculated. Results are compared against the limited numerical results available in the literature and indicate excellent agreement.

Equivalent circuits in Fourier space for the study of electromagnetic fields

Abstract: The introduction of properly defined and electric circuits in Fourier space can give a new powerful technique in studying problems of electromagnetic waves, and a novel view of the behaviour of these waves, in different applications. Using Parseval's identity theorem, one is able to obtain all the possible information for electromagnetic waves by its spatial Fourier transforms. Thus inversion in real space can be avoided completely. The authors present the theory and examples of this new technique in various applications of electromagnetic waves. The coincidence with already existing theoretical formulae or results is evidence that the proposed method is completely equivalent to the classical formulation. But, due to its simplicity, this technique could be very useful in studying electromagnetic field problems.

Maxwell's equations in the multipolar representation

Abstract: Arguments are given in support of a remark made by Mandel, that Maxwell's equations are not consistent with the multipolar form of the Hamiltonian for the electromagnetic field interacting with nonrelativistic electrons.

Analysis of finite dielectric bodies in a plane-wave field

Abstract: A new theoretical solution for studying the absorption of electromagnetic radiation by finite dielectric bodies is described. It combines the analytical eigenfunction-expansion method with a single surface integral equation. The method is applied to compute the electromagnetic fields inside a finite circular cylinder excited by a plane electromagnetic wave. The theoretical results are compared with the measured data, obtained by the authors, on cylinders of salt water.

Splines for electromagnetics

Abstract: The theory of splines for approximation is developed. The theory is presented in a general form applicable to other than just piecewise polynomial approximation. The relationship of spline approximation and finite elements is shown with an example given to demonstrate the procedure as applied to the solution of Poisson's equation. The use of spline functions in the method of moments is also discussed. The results of this use is then presented for the solution of a center-fed wire antenna.

Scattering Calculations Using The Extended Boundary Condition Method

Abstract: The extended boundary condition method (EBCM) is being used by many investigators to study a variety of electromagnetic (EM) problems such as the scattering of EM waves from non-spherical dielectric objects. This paper reviews briefly the theoretical development of EBCM involving the expansion of electromagnetic fields in terms of the vector spherical wave functions and solving the resulting matrix equations, and describes application of the method to specific problems: (1) scattering from layered objects, (2) near-zone scattering when both source and detector are near an object, and (3) fluorescent scattering resulting from active molecules embedded in an oblate spheroid.

Electromagnetic Generation and Ultrasonic Attenuation of Shear Waves in Potassium

Abstract: The magnetic field dependence of theelectromagnetic generation efficiency and theultrasonic attenuation of shear waves have been measured in potassium single c rystals at 4.2 K and 20 K. Electromagnetic transducers were used for both generation and detection of the ultrasound. The magnetic field dependence of the electromagnetic generation amplitude, the e lectronic contribution to the u ltrasonic a ttenuation and the ultrasonic absorption edges were studied for both the C’ and C44 shear modes. The observed zero-field generation amplitude is larger than thatpredicted by the free-electron theory. In addition, a non-monotonic field dependence of the electromagnetic generation amplitude for magnetic fields near and below the absorption edge has also been observed. The experimental results will be compared with previous measurements in potassium and with a theory of electromagnetic generation based on the free-electron model but assuming that electrons are scattered diffusely rather than specularly from the metal surface.