摘要:

We present an exact analysis for the electromagnetic coupling to a thin overhead cable from a vertical line current source terminated in a perfectly conducting ground plane. The spectral method employed permits a full satisfaction of the impedance boundary condition at the cable. The quasi-static limit of the obtained solution in the time domain, for the net cable current, is expressed in closed form. The results are relevant to the induced currents on power and communication lines.

ISSN:0920-5071    

DOI:10.1163/156939398X01222

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A design procedure for a microwave absorber is presented. The absorber consists of two lossy planar layers on a conducting plate. One of the layers is magnetically lossy while the other is electrically lossy. With a prescribed percentage of power loss in each layer and a partial knowledge of the layer parameters, a complete design procedure is outlined. It is shown that the bandwidth over which the reflection loss is above a certain limit depends on the ratio of power loss in the two layers. It is shown that high reflection loss can be achieved over frequency ranges as high as 3:1 ratio.

ISSN:0920-5071    

DOI:10.1163/156939398X01231

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The dependence of resistivity on pressure is well known in water saturated porous sedimentary rocks. A new electromagnetic fractal model has been employed successfully to study the fractal parameters for double layer polarisation in the low-to-intermediate frequency range. This model addresses the roughness of the pore space and it has been employed to study the over burden effects on the complex resistivity under in situ conditions in the frequency range 10Hz-100kHz and pressure range 1MPa-40MPa. This model includes three relaxation times: bulk relaxation, double layer relaxation and fractal relaxation of pore roughness surfaces; a grain ratio resistivity relating the resistivity of blocking grains to the electrolyte resistivity; the DC resistivity of the rock; the chargeability; and the fractal frequency exponent given by the fractal nature and roughness of the pore surfaces.

ISSN:0920-5071    

DOI:10.1163/156939398X01240

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Maxwell's equations for a laterally periodic inhomogeneous structure are considered. The transmission Green's function approach based on a vacuum wave-splitting is used to solve the scattering problem. A dielectric grating is considered first. The direction of the incident plane wave is arbitrary, and numerical results for the co- and cross-polarized reflection and transmission for TE and TM waves are presented. The approach is also generalized to the scattering from a bi-anisotropic grating.

ISSN:0920-5071    

DOI:10.1163/156939398X01259

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The adaptive integral method (AIM) is applied to the scattering and radiation analysis of arbitrarily shaped planar structures. The method extends the well-known conjugate gradient fast Fourier transform (CGFFT) method to the triangular subdomain discretization, which has a much better geometry modeling capability than the rectangular subdomain discretization employed in the traditional CGFFT method. The resulting algorithm has a memory requirement proportional to O(N) and the operation count for the matrix-vector multiplication proportional to O(N log N). Numerical results are presented to demonstrate the efficiency and accuracy of this method.

ISSN:0920-5071    

DOI:10.1163/156939398X01268

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

As a prelude of three-dimensional modeling of a submarine, an analysis of degaussing of a two-dimensional magnetic cylinder is presented in this paper. The cylinder is of infinite length and may be of arbitrary cross section. As the first step of determining the degaussing current needed for minimizing the magnetic field of the cylinder, a free surface current is assumed on the cylinder surface. Under the influence of the magnetic field produced by the assumed surface current, the cylinder is magnetized and a magnetization current is induced on its surface. An integral equation is formulated for the unknown magnetization current, with the magnetic field due to the assumed surface current as the forcing function. The integral equation is solved numerically employing the moment method. Then, based on knowledge of the magnetization current, the magnetic field produced by the cylinder is calculated. The magnetic field of the cylinder which is magnetized by the assumed surface current is compared with the field of the same cylinder but magnetized in the earth's magnetic field. The ratio of the magnetic flux density of these two fields is taken as the "scaling" factor for determining the degaussing current needed. Numerical results are presented and discussed. In particular, data for a circular cylinder are compared with the analytical results obtained based on image theory. To illustrate the effectiveness of the degaussing system, the magnetic flux density of a magnetic cylinder after applying the degaussing current on its surface is compared to that without the degaussing current.

ISSN:0920-5071    

DOI:10.1163/156939398X01277

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The concept of propagation matrix is generalized to a two- break dimensional inhomogeneous thin layer. The first order and second order propagation matrices are derived with a scaling method through an asymptotic expansion as a power series of the thickness. The generalized propagation matrix is verified in several special cases when the propagation matrix has an exact and explicit form.

ISSN:0920-5071    

DOI:10.1163/156939398X01286

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This paper presents an adaptive multiscale moment method for the analysis of electromagnetic scattering from perfectly conducting two dimensional strips. The advantage of this method is that the number of unknowns can be reduced by setting a threshold as is usually done in wavelet analysis. The novelty of this approach is that the threshold is applied dynamically in an adaptive fashion. It is applied to the unknowns directly by utilizing results of the previous scales and thereby significantly reducing the number of unknowns that is to be solved for. Typical numerical results are presented for some TE and TM cases of electromagnetic scattering from the perfectly conducting strips to illustrate the efficiency of this approach.

ISSN:0920-5071    

DOI:10.1163/156939398X01295

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A unified electrodynamic approach to the guided wave excitation by external sources in waveguiding structures with bianisotropic media is developed. Effect of electric, magnetic, and magneto-electric losses in such media manifests itself in the special form of eigenmode orthogonality referred to as the quasi-orthogonality relation. It reflects the existence of the cross-power flow Pkland loss Qklfor any pair (k, l) of modes which are rigidly linked to each other by this relation. The quasi-orthogonality relation remains true in the limiting case of lossless waveguides yielding the customary relations of orthogonality and normalization for propagating (active) modes and also their generalization for nonpropagating (reactive) modes. It is shown that the eigenmode set for a waveguiding structure is complete only outside the region of exciting sources. Inside this region the modal expansions of fields are incomplete and must be supplemented with the orthogonal complementary fields which extend the proper Hilbert space spanned by waveguide eigenfunctions. Among exciting sources there are the external bulk sources (currents, fields, and medium perturbations) and the external surface currents. Besides, the orthogonal complementary fields generate the effective surface currents on boundaries of the bulk exciting sources. The problem of waveguide excitation by external sources is solved by means of determining both the mode amplitudes for the modal field expansions and the orthogonal complementary fields inside the source region. The equations of mode excitation are derived on the basis of three approaches applying the direct use of Maxwell's equations, the electrodynamic analogy with the mathematical method of variation of constants, and the reciprocity theorem in conjugate form.

ISSN:0920-5071    

DOI:10.1163/156939398X01303

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A unique Fourier series approach to the problem of computing currents excited on a conducting bent wire enclosed in a shielded enclosure is presented. The wire is folded at right angle and oriented in a plane parallel to one of the cavity walls. Electromagnetic sources exterior to the cavity excite one end of the wire, while the other end of the wire within the cavity may have any arbitrary load conditions. The coupling between the two portions of the bent wire, which are perpendicular to each other, is taken into consideration. The formulation of this problem makes use of the theory of Fourier series to approximate the waveform of unknown current excited on the wire. Of course, the infinite Fourier series is approximated by a truncated Fourier cosine series in order to obtain an analytically simple solution. The number of Fourier series coefficients and the cavity modes are the key issues to the formulation. Selected numerical results in the form of current distributions are presented to illustrate the formulation. This formulation can easily handle any arbitrary load condition.

ISSN:0920-5071    

DOI:10.1163/156939398X01312

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor