摘要:

Scattering of electromagnetic waves from arbitrary shaped dielectric particles that are small compared to the wavelength in surrounding medium is studied theoretically by means of the local perturbation method generalized for vector equations. The resonance conditions are formulated, and the resonant frequency and the width of the resonance are calculated. As an example scattering of electromagnetic waves radiated by a moving charged particle is considered.

ISSN:0920-5071    

DOI:10.1163/156939300X00789

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper presents an efficient full wave numerical analysis method for three dimensional microstrip structures inside a stratified media. The method can analyze both vertical and horizontal components of the currents. The conducting structures are modeled using a mixed potential integral equation. The boundary conditions on the interfaces between dielectric layers are satisfied through the use of appropriate dyadic Green's functions in the spectral domain. The numerical evaluation of the Sommerfeld integrals that are encountered during the transformation of the Green's function to the spatial domain is avoided using the complex images method (CIM). A modified CIM is proposed for efficient solution of vertical conductors currents. The modification maintains the rigorous nature of the full-wave analysis method while achieving the same efficiency for both vertical and horizontal components of currents. The resulting algorithm is found to be a versatile and efficient numerical analysis tool for microstrip antennas. The accuracy of the method is tested against commercially available full wave analysis packages. Good agreement is obtained for a wide class of stacked microstrip antennas.

ISSN:0920-5071    

DOI:10.1163/156939300X00798

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The propagation of transient waves is considered along the principal axis of symmetry in a magnetic crystal. The occurrence of magnetoelectric effects, characterized by skew-symmetric susceptibilities, gives rise to wave modes propagating in opposite directions with different speeds and different amplitude attenuation. The wave propagators are evaluated for each mode through an asymptotic expansion of the Laplace transforms of the constitutive functions. Thermodynamic restrictions on these functions are shown to impose wave damping due to time dispersion and to the presence of electric conductivity. Reflectivity at a discontinuity surface within the magnetic material is also investigated in detail. Dissipative effects are shown to characterize the behaviour of the reflected field.

ISSN:0920-5071    

DOI:10.1163/156939300X00806

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In this paper, we present an inverse scattering approach based on a neural network technique for the detection of dielectric targets buried in a lossy half-space. In particular, we focus the attention on the analysis of the neural network capability to localize a given cylinder starting from the known values of the electromagnetic scattered field evaluated at a number of points near the half-space interface. The robustness of the developed technique is firstly tested by considering a target and/or an electromagnetic scenario characterized by dielectric parameters different from those used during the training phase and secondly by using noisy input data.

ISSN:0920-5071    

DOI:10.1163/156939300X00815

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We examine wave scattering by a perfectly conducting periodic surface, and demonstrate that for vertical polarization, conventional perturbation theory is invalid in the presence of a low-grazing scattered mode. We develop a new perturbation expansion that is valid when one of the scattered modes propagates at a low grazing angle. For this expansion, scattering amplitude is nonlinear in height. We find that the surface is conveniently characterized by effective impedance and corresponding Brewster angle. Conventional perturbation theory is valid only when all scattering grazing angles are larger than the effective Brewster angle, and new perturbation formulas are accurate when one mode is below the effective Brewster angle. This development resolves any contradiction between low-grazing scattering results by Barrick [1] and Tatarskii/Charnotskii [2, 3], for a periodic surface case. We propose a uniform perturbation approximation which combines the conventional and low-grazing-angle perturbation results and incorporates the effective surface impedance. In particular, this theory describes the sign change of the reflection coefficient when the incidence angle approaches zero.

ISSN:0920-5071    

DOI:10.1163/156939300X00824

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We examine wave scattering by a perfectly conducting periodic surface in the presence of two diffraction modes propagating at low grazing angles. This scenario includes a backscatter case that has practical importance. For TM polarization, conventional perturbation theory is shown to be invalid in the limit of small grazing angles. We develop a new perturbation expansion that is valid when two of the scattered modes propagate at low grazing angles. We find that there is a critical scattering angle associated with the surface profile. Conventional perturbation theory is valid only when all scattering grazing angles are larger than the critical angle, and new perturbation formulas are accurate when two modes are below the critical angle. This development resolves the existing contradiction between low-grazing backscattering results by Barrick [1] and Tatarskii/Charnotskii [2, 3] for a periodic surface case. We propose a uniform perturbation approximation which combines the conventional and low-grazing angle perturbation results and incorporates the critical angle. This theory accurately describes the sign change of the reflection coefficient when the incidence angle approaches zero as well as a sharp decrease in the reflection coefficient at the critical angle.

ISSN:0920-5071    

DOI:10.1163/156939300X00833

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An extension to a previous approach is presented in order to treat the 2D TM-scattering from a multiangular groove engraved in a perfectly conducting plane. The domain product technique is used to construct solution of the problem in the interior of the channel. The efficient field representation, adapted to studying composite cylindrical structures with polyhedral boundaries consisting of conducting parts and interfaces, is proposed. The sought-for quantities inside and outside the cavity are expressed in terms of the Mathieu function expansions. Boundary value problem is reduced to solving a system of infinite matrix equations of the second kind with respect to the expansion coefficients. The validity and efficiency of the approach have been checked and confirmed for the case of a rectangular groove. Examples dealing with the arbitrary cavities are presented.

ISSN:0920-5071    

DOI:10.1163/156939300X00842

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An asymptotic high frequency solution is presented for the problem of electromagnetic wave diffraction by an open-ended parallel plate waveguide cavity with impedance walls, using the Wiener-Hopf techniques. By using the 'image bisection principle' the original problem is converted into two simpler ones. By expanding the total field in the waveguide region into a series of normal modes and using the Fourier transform techniques elsewhere, one obtains a modified Wiener-Hopf equations (MWHE) of the third kind for each excitations. The solution of these MWHE can explicitly be obtained by solving infinite number of constants satisfying an infinite system of linear algebraic equations. Representative numerical examples, illustrating the

ISSN:0920-5071    

DOI:10.1163/156939300X00851

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The problem of propagation in sea water of a low-frequency pulse excited by a Hertzian electric dipole is revisited. The source current is generated via the sinusoidal modulation of a continuous exponential pulse with finite rise and decay times. Simple asymptotic formulas are derived for the electric field in the equatorial plane of the dipole for times and distances of practical interest.

ISSN:0920-5071    

DOI:10.1163/156939300X00860

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A theoretical and numerical investigation is carried out in order to evaluate the impact of the atmospheric emission on passive microwave polarimetric measurements of the ocean wind vector. The apparent full Stokes vector at the top of the atmosphere, due to both the surface and atmospheric brightness temperatures, is derived for an azimuthally anisotropic sea surface. The atmospheric upwelling

ISSN:0920-5071    

DOI:10.1163/156939300X00879

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor