摘要:

A theory is developed for the propagation of plane electromagnetic waves with a narrow-band spectrum in weakly nonlinear media. Representation of a wave as a set of harmonics with slowly spatially-varying amplitudes and spectrum parameters allows us to obtain evolutionary equations for these parameters. This yields a description of energy migration between harmonics, and also their spectrum and wave-envelopes transformation. Forming of harmonic pulses (spectra) in the near zone and the asymptotic behavior in the far zone, including conditions of pulses compression (or stretching) are investigated.

ISSN:0920-5071    

DOI:10.1163/156939396X00018

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The dyadic Green's functions (DGF's) of a two-layer biaxially anisotropic medium are derived. The principal coordinate system of the anisotropic medium is allowed to have arbitrary orientation with respect to the layer geometry. First, the unbounded DGF is derived using the Fourier transform method. Hence the DGF's for the two-layer medium in the spectral domain are formulated. Using a matrix method the coefficients of the two-layer DGF's are expressed in terms of half-space Fresnel reflection and transmission coefficients. To complete this procedure the various relevant half-space Fresnel coefficients are derived. The form in which the results are presented has a physically meaningful and compact structure. A numerical example is provided where we have computed the reflectivities.

ISSN:0920-5071    

DOI:10.1163/156939396X00027

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The theory for solving of singular integral equations (s.i.e) in the class of singular functions is given briefly. The antenna-diffraction problem (a.d.p.) is presented as an example. The solution of this problem can be reduced to the considered integral equation type. It is shown that the theory can be applied to solution for the problem of removing "luminescence" of contour angle points by location of current sources on a contour near these points. Amplitudes of these sources are selected in a special manner. One can control the scattering diagram with the help of known amplitudes of other sources. The numerical methods for the solution of the considered integral equations are elaborated. The examples of calculations for the mentioned above physical effects are given.

ISSN:0920-5071    

DOI:10.1163/156939396X00036

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We develop an optimal control algorithm, using a BI method, in order to obtain the most favourable RAM coating on a given 3D perfectly conducting scatterer, minimizing its monostatic RCS. The RAM is simulated using a first order impedance boundary condition with a scalar surface impedance corresponding to an isotropic passive structure and defined pointwise on the surface. The optimality system, resulting from a Lagrangian approach, turns this complex problem into a sequence of line searches through standard descent methods. Then we may compute an optimal solution corresponding to a local minimum of the scatterer's RCS according to several electromagnetic configurations.

ISSN:0920-5071    

DOI:10.1163/156939396X00045

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Solutions to two-dimensional electromagnetic imaging problems have been investigated extensively in recent years. Three-dimensional imaging problems have not been as well researched due to the inherent complexity of the formulation. Moreover, most of the work on imaging has concentrated on targets embedded in free space. In this paper, a technique for three-dimensional imaging based on an iterative Born method is presented. Targets with higher dielectric contrast for which the linear Born approximation is not valid can be imaged by using multiple iterations with this method. The extension of the technique to image a target buried in an inhomogeneous background is achieved by evaluating numerically the dyadic Green's function. Numerical simulations are presented to illustrate the applicability of the imaging algorithm. The results for a simulation are compared against those obtained with the inverse source method, and the difference in the performance of the two techniques is discussed. The convergence of the Born iterative method is also investigated in this paper.

ISSN:0920-5071    

DOI:10.1163/156939396X00054

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The sharp variations of the electromagnetic wave amplitude are analyzed in the section of the meander or strip line made of pure aluminum. These variations appear at low temperatures when high magnetic field and strong pulses of electric current are parallel. The pulses containing two switching waves are observed. The propagation velocity of this pulses is approximately 106cm/s. At certain conditions the auto-wave electrodynamical structure arises in high magnetic field. It has been suggested the system of equations that can to explain the main experimental features.

ISSN:0920-5071    

DOI:10.1163/156939396X00063

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

In a wave framework, eddy current nondestructive evaluation of a void defect in a conductive half-space is attempted from aspect-limited, frequency-diverse data. As a first step a linearized version of this non-linear, ill-posed inversion problem is considered. The test zone is modeled as a distribution of cells either black (void) or white (metal)- an inclusion of known, constant conductivity could be considered similarly. The optimal distribution is such that the minimum of a cost function made of the quadratic difference between data and replica fields plus two regularization terms, one linked to the size of the defect, the other to its connectivity, is reached. A simulated annealing algorithm is used to do so. Salient features of the evaluation procedure are illustrated by examples from both noiseless and noisy synthetic data, in particular the fact that the connectivity constraint results in a faster retrieval of a more "compact" anomaly.

ISSN:0920-5071    

DOI:10.1163/156939396X00072

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Scattering of TM waves from a cylindrical scatterer embedded inside a two-layer lossy ground under the assumption of a sinusoidal air-ground interface is investigated. The problem is formulated via an integral equation approach combined with the extended boundary conditions method. The integral equation over the cross section of the scatterer is transformed into an infinite set of linear equations for the expansion coefficients of the unknown magnetic field inside the scatterer. This set is truncated and solved numerically. The numerical results obtained for the far-zone scattered field show that it is is mainly affected by the characteristics and the position of the scatterer with respect to the dips and lifts of the rough surface as well as by the conductivity of the surrounding ground layers. In certain cases the scattering pattern provides useful information about the position and the type of possible buried scatterers.

ISSN:0920-5071    

DOI:10.1163/156939396X00081

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939396X00090

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939396X00108

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor