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.

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

Electromagnetic Penetration Through Apertures in Conducting Surfaces

The general 3-D aperture coupling problem is formulated in terms of an integral equation for the equivalent magnetic current in the aperture, which is numerically solved by the method of moments. The aperture is characterized by two aperture admittance matrices, one for the exterior region and the other for the interior region. These two admittance matrices are determined separately but in a similar manner if the pseudo-image method is used. Numerically workable expressions are developed for the two aperture admittance matrices by decomposing each of them into a half-space admittance matrix and a supplementary admittance matrix. The half-space admittance is relatively easy to compute and has been investigated in the literature. The supplementary admittance matrix is expressed in terms of the generalized impedance combining the existing numerical codes for an arbitrarily shaped scatterer and for an arbitrary aperture in a conducting plane, one can obtain a code which is especially designed for an arbitrary aperture in a conducting surface of arbitrary shape. >

Electromagnetic scattering from and transmission through arbitrary apertures in conducting bodies

For an E-polarized plane wave incident on a perfectly conducting cylindrical shell having a longitudinal slit aperture, the fields inside the cavity are determined by a numerical solution of the E-field integral equation. Selected data are presented and the first few complex frequency (SEM) singularities are determined for a variety of aperture sizes.

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Electromagnetic Field Penetration into a Cylindrical Cavity

The problem of the scattering of an electromagnetic plane wave with arbitrary polarization and angle of incidence from a perfectly conducting spherical shell with a circular aperture is solved with a generalized dual series approach. This canonical problem encompasses coupling to an open spherical cavity and scattering from a spherical reflector. In contrast to the closed sphere problem, the electromagnetic boundary conditions couple the TE and TM modes. A pseudodecoupling of the resultant dual series equations system into dual series problems for the TE and TM modal coefficients is accomplished by introducing terms that are proportional to the associated Legendre functions P−m0. The solutions of the TE and TM dual series problems require the further introduction of terms proportional to P−mn, where 0≤n<m. These functions effectively complete the standard spherical harmonic basis set when an aperture is present and guarantee the satisfaction of Meixner’s edge conditions. Having generated the modal coeffic...

Electromagnetic scattering of an arbitrary plane wave from a spherical shell with a circular aperture

A plane wave is symmetrically incident on a spherical shell with a circular aperture. The fields inside and outside the cavity are expanded in terms of spherical vector wave functions and the modal coefficients are found by application of the least squares method to the boundary conditions. Computed data are obtained and the results exhibited in the form of amplitude curves of the interior and aperture fields as functions of position for a variety of cavity and aperture sizes. Within the cavity it appears that the field variations are primarily determined by the cavity size and that the aperture size serves only to scale them.

Gerard A. Desjardins

Papers

Electromagnetic Field Penetration into a Spherical Cavity