Chalmers M. Butler

Electromagnetic penetration through apertures in conducting surfaces

In designing hardened systems, one must be able to characterize as well as quantitatively determine the penetration of EMP signals through apertures of general shapes in structures of varying configurations. In this paper a tutorial review of a number of methods for analyzing such aperture problems is presented with an emphasis on techniques. The discussion presented herein is reasonably self-contained and is supplemented by references to classical as well as current approaches to the aperture problem. An extensive set of representative numerical results is included.

Analysis of various numerical techniques applied to thin-wire scatterers

Several numerical schemes for solving Pocklingtons and Hallens equations for thin-wire scatterers are investigated. Convergence rates of solutions obtained from seven methods are given and reasons for different rates are delineated.

The equivalent radius of a narrow conducting strip

By means of a simple and direct analytical procedure, it is confirmed that the equivalent radius of a narrow conducting strip is one-fourth its width. The analysis proceeds from the integral equation for the surface current density induced on a conducting cylinder of general cross section and its incorporates knowledge of the current density induced on a narrow strip. Explicit expressions are given for the total axial current induced on the narrow strip and for its echo width.

General analysis of narrow strips and slots

The general problems of TE- and TM-excited slots in screens and conducting strips whose widths are narrow relative to the wavelength are investigated. The narrow width approximation is imposed upon the slotted-screen and strip equations from which result approximate equations that are solved exactly. For general excitation, solutions are presented for both polarizations as products of series of Chebyshev polynomials and appropriate singular functions exhibiting the known edge condition. Special attention is afforded the problem of the slot/strip excited by illumination which can be represented by two terms of a Taylor series due to the practical importance of this situation.

Electromagnetic excitation of a wire through an aperture-perforated conducting screen

Integro-differential equations are formulated for the general problem of a finite-length wire excited through an arbitrarily shaped aperture in a conducting screen. The wire is assumed to be electrically thin and perfectly conducting, and it is arbitrarily oriented behind the perfectly conducting screen of infinite extent. A known, specified incident field illuminates the perforated-screen/wire structure. The integro-differential equations fully account for the coupling between the wire and the aperture/screen. They are specialized to the case of the wire parallel to the screen with the aperture a narrow slot of general length. These special equations are solved numerically and data are presented for wire currents and aperture fields under selected conditions of wire/slot lengths and orientation. Data indicative of the coupling between the wire and slot are presented.

Evaluation of potential integral at singularity of exact kernel in thin-wire calculations

A technique is presented for calculating the potential integral of thin-wire theory at the singularity of the exact kernel in cases where the current is representable as piecewise constant and/or piecewise linear over an interval containing the singularity. The integral of the rapidly varying portion of the kernel is converted to a highly convergent power series. Examples of how one employs the results in computations are given.

Electromagnetic Penetration Through Apertures in Conducting Surfaces

In designing hardened systems, one must be able to characterize as well as quantitatively determine the penetration of EMP signals through apertures of general shapes in structures of varying conflgurations. In this paper a tutorial review of a number of methods for analyzing such aperture problems is presented with an emphasis on techniques. The discussion presented herein is reasonably self-contained and is supplemented by references to classical as well as current approaches to the aperture problem. An extensive set of representative numerical results is included.

EFFECTIVE METHODS FOR SOLVING INTEGRAL AND INTEGRO-DIFFERENTIAL EQUATIONS

ABSTRACT Effective numerical methods for solving simple integral and integro-differential equations with logarithmically singular kernels are presented tutorially in this paper. Fundamental features and interrelationships of the methods are discussed. Procedures for applying the techniques to practical equations of electromagnetics are suggested.

An alternate frill field formulation

An alternate form [1] for the near zone E_{z} fields of an annular ring of magnetic current is derived. The new expression avoids numerical differentiation, offers significant improvements in efficiency, and is particularly useful in the analysis of coaxially driven parallel arrays.

Currents induced on a pair of skew crossed wires

Hallen-type integral equations are formulated for skew crossed wires and, by numerical solution techniques, current distributions are obtained. The coupled integral equations are founded entirely upon the familiar electric scalar potential and magnetic vector potential whereas, in the past, similar analyses have been based upon an auxiliary scalar function. Numerical results are presented for several cases, including different skew angles, and are compared with available data for the special case of perpendicular wires.