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Electromagnetic scattering by a two-dimensional inhomogeneity due to an oscillating magnetic dipole

Description: A numerical method of computing the electromagnetic response of two-dimensional earth models to an oscillating magnetic dipole is presented. The generalized electromagnetic variational integral is reduced to a sum of two-dimensional variational integrals by Fourier transformation. Discretization of each two-dimensional integral is carried out in terms of the secondary electric fields by using the finite element method. Following the variational principle, each harmonic integral is reduced to a set of simultaneous equations. From each set of electric field solutions obtained by solving the simultaneous equations, the secondary magnetic fields are computed numerically. After inversely Fourier transforming the secondary electric and magnetic fields, the total fields are finally obtained by adding the analytically calculated primary fields. Because of the systematically implied continuity of the electric field in the finite element solution, the given discontinuous conductivity is modified to a continuous one across internal boundaries. The quality of the solution for the horizontal magnetic dipole is found to be relatively poor compared to that for the vertical magnetic dipole. It is not possible to perform an absolute numerical check of the solution due to the lack of another independently developed solution against which it can be checked. As an alternative the solutions for two-dimensional models were compared to those for some elongated three-dimensional models whose cross sections correspond to the two-dimensional models. 23 figures, 1 table.
Date: September 1, 1978
Creator: Lee, K.H.
Partner: UNT Libraries Government Documents Department

Experimental study of the use of Bethe hole theory for wires behind apertures

Description: This report presents an experimental validation of the use of Bethe hole theory in the numerical modeling of apertures in structures with wires behind the apertures. Three configurations are examined in this study: thin, capped cylinders with the wire located along the cylinder center; apertures in a plane with a wire; and fat, capped cylinders with wire inside. Currently accepted methods that use the Bethe hole theory to model the aperture are used to model numerically the current on the wires. The numerically generated current data are compared with experimental results. This validation is performed for both electrically small and large apertures. 55 figures, 5 tables.
Date: March 23, 1978
Creator: Brittingham, J.N.; Deadrick, F.J. & Lager, D.L.
Partner: UNT Libraries Government Documents Department