摘要:

It is well known that the natural frequencies of an object are important distinguishing features which can be used in target detection and discrimination schemes. These natural frequencies are governed by the size, shape, and material composition of the object, as well as the environment in which the object resides. Since a given object of interest may reside in many different environments, it is of interest to relate the natural frequencies of an object when in free-space to the natural frequencies of the same object when immersed in a non-homogeneous environment. In this paper a perturbation formula is developed which relates the free-space natural frequencies of an object to those of the same object in the presence of a planarly layered medium. The perturbation formula is valid for intermediate spacing between the object and the nearest planar interface. Numerical results are shown for the natural frequencies of a wire in the presence of a layered medium.

ISSN:0272-6343    

DOI:10.1080/02726349808908593

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Only in a few cases of special symmetries, an analytic solution of Maxwell's Equations together with appropriate boundary conditions can be found. Among other things, difficulties occur because Maxwell's Equations represent a set of coupled partial differential equations (PDEs). Therefore, methods have been developed to convert the PDEs with boundary conditions into a set of ordinary DEs. This simplification usually goes along with a loss of accuracy. In this paper, the prerequisites for the derivation of (stochastic) Generalized Telegraphist's Equations (GTEs) for (irregular) deformed waveguides are discussed. It turns out that a systematic approximative derivation of GTEs is only possible in rare cases. In any case, further knowledge about the fabricational cause of the surface imperfections is needed to fix the stochastic properties of the GTEs. The method's application to an irregular deformed helix is used as an illustrating example.

ISSN:0272-6343    

DOI:10.1080/02726349808908594

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We present a novel algorithm for determining the fundamental modes and cutoff wavenumbers in metallic waveguides with arbitrary cross-section, possibly loaded with inhomogencous dielectrics. The method is based upon a generalized Donskcr-Kač formula which leads to a closed-form expression for the sought quantities in terms of asymptotic generalized Wicncr-to integrals. These path integrals arc computed by means of Monte Carlo methods, leading to a completely parallel algorithm with mild memory requirements. The method can be easily generalized to 3D problems including electromagnetic resonators.

ISSN:0272-6343    

DOI:10.1080/02726349808908595

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Electromagnetic sources in a uniaxial anisotropic medium are known to be decomposable in two parts producing fields with TE and TM polarization with respect to the axis of the medium. Also, an expression for the Green dyadic in the same medium has been derived. In this study, these two solution principles are brought together by finding the TE/TM decomposition of the Green dyadic. This is done by finding the solution for the ensuing fourth-order partial differential equations in analytic form. In addition to being conceptually attractive, the new decomposed expression is helpful in solving electromagnetic problems with either TE or TM character, in which case only one of two components of the Green dyadic is needed.

ISSN:0272-6343    

DOI:10.1080/02726349808908596

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

All dielectrics, by nature are dispersive. This frequency dependence of materials must be modelled whenever microwave structures are expected to operate over broad bands of frequency. The Analytic Continuation Model of materials meets this need. As a compact, complete, ultrabroadband representation of all physically realizable dielectrics, this model can be used for the analysis and design of realistic electromagnetic engineering structures. The model represents dispersive materials as a sum of special complex functions reducible to analytic circuits. After a brief derivation of the model, an approach for obtaining the parameters of the circuits, in the case of dispersive radiofrequency materials, is disclosed. Its use is demonstrated by obtaining a model of a carbon loaded foam that is valid over a 2,000,000:1 bandwidth. The model is then applied to the problem of synthesizing materials with prescribed frequency dependent permittivity profiles for the modification of the electromagnetic properties of structures. Illustrative examples are solved using a Dispersive Finite Difference Time Domain computer code to demonstrate the simplicity and versatility of the model.

ISSN:0272-6343    

DOI:10.1080/02726349808908597

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Methods and results of experimental investigations of novel bianisotropic omega composites are discussed in this paper. Samples of omega composites are tested in waveguide and in free space. Reflection and transmission coefficients are the subject of interest. The results of the theoretical modeling and the experiment are compared for layered omega structures. The experiments confirm the first theoretical recommendations on optimizing properties of omega slabs.

ISSN:0272-6343    

DOI:10.1080/02726349808908598

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor