摘要:

The effect of eccentricity on the complex resonances of a conducting sphere eccentrically coated by a dielectric one is investigated. The solution of the boundary value problem is obtained in terms of spherical eigenwaves in combination with the translational addition theorem. The resonant wavenumbers are calculated from the numerical solution of a characteristic determinantal equation. The analysis is also specialized to the case of small eccentricity and closed form expressions are derived for the resonant wavenumbers. It is found that the restriction of small eccentricity is not severe. It is also found that under the influence of eccentricity the resonant wavenumbers are considerably displaced in the complex plane. This may be used in the identification of the position and the size of inhomogeneities inside spherical bodies.

ISSN:0920-5071    

DOI:10.1163/156939397X00611

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The physical restrictions for the constitutive parameters of chiral media are looked for and tested against available measurement data. These restrictions include Kramers-Kronig relations for the constitutive parameters of isotropic chiral media and conditions developed from the wave propagation characteristics and the energy principle. The restrictions are applied to wideband measurement data of an isotropic chiral slab.

ISSN:0920-5071    

DOI:10.1163/156939397X00620

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We present a new analytical approach for scattering from perfectly conducting surfaces that are rough in one dimension. The method is based on expanding the Helmholtz equation using a set of local basis functions. The transformed equations contain the field and its normal derivatives at the surface as source functions. The first order approximate solution, sought for slightly rough surfaces, is obtained using the local tangent plane approximation at the surface. It is shown analytically that the new method reduces to the first order perturbation method in the proper limit. A systematic series solution is proposed using perturbation theory in conjunction with the present formulation. The second order result is given and analyzed. The results of the present theory are not reciprocal and a reciprocity rule is formulated to overcome this disadvantage. We compare numerically the bistatic scattering cross section for Gaussian-randomly rough surfaces predicted by the first order solution with numerical results and other first order theories. It is shown that the present formulation is overall more accurate than other existing theories.

ISSN:0920-5071    

DOI:10.1163/156939397X00639

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The radiation characteristics of an axial slot on a circular conducting cylinder with reflector wings are investigated. Integral equations for both TM and TE cases are derived using Green's SECOND identity. The method of moments is then employed to obtain a numerical solution for the integral equations. Comparison with the published data of slot on a circular cylinder and slotted cylinder in a ground plane showed an excellent agreement. Several radiation patterns corresponding to new geometries of the antenna are then presented.

ISSN:0920-5071    

DOI:10.1163/156939397X00648

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

An analytically simple and efficient approach to the analysis of multiple wires in a rectangular cavity is developed. This approach addresses the coupling characterization of the multiple wires in terms currents induced on them by applying thin wire approximation. Electromagnetic sources exterior to the cavity excite at least one of the wires. The formulation of this problem makes use of the theory of Fourier series to approximate the waveform of unknown currents excited on each wire. The field distribution within the cavity is determined utilizing the orthogonality properties. Finally, a matrix equation for the unknown Fourier coefficients is obtained by enforcing appropriate boundary conditions on the axis of the wires. The interaction among the wires is taken into account. Selected numerical results are included to illustrate the effects of various conditions, namely, the load and the locations of the wires in the cavity.

ISSN:0920-5071    

DOI:10.1163/156939397X00657

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This paper continues to discuss the coupling characterization of multiple wires of arbitrary dimensions in terms induced on currents on them enclosed in a rectangular cavity. The formulation of this problem also makes use of the Fourier Series method to compute currents induced on each wire. In the thick wire approximation, the current is still assumed to reside on the wire axis, but the boundary condition is enforced on four generatrices spaced around the circumference of the wire. Selected numerical results are included for a variety of diversified situations in the cavity environment.

ISSN:0920-5071    

DOI:10.1163/156939397X00666

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The Trapezoidal Recursive Convolution (TRC) scheme was previously used to model Nth order Lorentz type dispersive media. In this paper, the full derivation of this quasi-trapezoidal-based algorithm is presented and the derivation is expanded to include the Nth order Debye type dispersion as well as Sellmeyer's dispersion equation. In addition, the case of general convolution integrals is considered where any arbitrary integrand or the integral itself is represented as a sum of exponential functions, i.e. Prony's method. The technique is compared to several previously published schemes and it is shown that its performance equals or exceeds various other methods in terms of accuracy, robustness, and computational efficiency. A comparison to the exact application of trapezoidal numerical integration is made and it is shown that, for time increments encountered in typical FDTD analyses, the truncation error due to applying the quasi-trapezoidal approximation is negligible. Finally, it is shown how the skin effect phenomenon, as it applies to multiconductor transmission lines, can be modeled using a rational function approximation to the frequency dependency of the line resistance. This model is obtained by using Levy's method to curve fit the line resistance directly in the frequency domain and then the convolution integral is formulated in a form amenable to the TRC algorithm.

ISSN:0920-5071    

DOI:10.1163/156939397X00675

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The operational calculus originally introduced by Heaviside is shown to be directly applicable to forming image principles for various electromagnetic structures. the image expression is reduced to the compact form of a pseudo-differential operator applied to the original source function (for a point source this is the delta function). The final step is an interpretation of this result. For complicated operators an approximation can easily be done at this stage. The Heaviside method replaces previously applied, often heuristic, identification processes by a logical procedure. The method is first applied to symmetric and asymmetric transmission-line problems because they arise from three-dimensional physical problems. Two examples are worked through: the time-harmonic planar problem of two isotropic media and the elctrostatic problem of the sphere. Both examples give results which have been previously derived through more heuristic methods. A table of selected operational formulas is given as an appendix.

ISSN:0920-5071    

DOI:10.1163/156939397X00684

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Coupling is studied between the dipole moments of electrically small bianisotropic particles. The interaction is defined and computed using a multipole expansion of the fields re-radiated by surrounding particles. The result is cast in the form of a six-vector bilinear form containing the interaction six-dyadic of the system which depends on the dipolarisability dyadics of the particles and their separation distance vector. In an alternative approach, the effect of coupling between the induced dipole moments is quantified by employing a de-embedding procedure. This leads to modified dipolarisability dyadics, which contain the dipolarisability dyadics of the individual particles and the separation distance vectors. These can be used with existing mixing rules to compute the effect of particle interaction on the constitutive parameters of the effective medium.

ISSN:0920-5071    

DOI:10.1163/156939397X00693

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939397X00701

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor