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Accurate Modeling Of The Electromagnetic Scattering Of Complex Dispersion Medium

Posted on:2014-04-24Degree:DoctorType:Dissertation
Country:ChinaCandidate:X AiFull Text:PDF
GTID:1228330431462464Subject:Electromagnetic field and microwave technology
Abstract/Summary:PDF Full Text Request
In recent years, with the in-depth study of electromagnetic theory and engineeringtechnology, as well as a wide exploration in the mechanism of interaction ofelectromagnetic wave with complex electromagnetic materials, the scatteringcharacteristic of complex dispersion medium, including the metamaterials as arepresentative of artificially synthesized electromagnetic material, the hypersonic plasmasheath and ionosphere as representatives of nature electromagnetic material, has drawngreat attentions in various research fields.In this thesis, two different methods have been proposed to improve the accuracy ofthe dispersive (or frequency dependent) FDTD scheme. One of the two methods is tointroduce higher-order algorithm into the dispersive FDTD algorithm, with which thenumerical dispersive error is depressed so as to improve the accuracy of dispersive FDTDscheme. And the second method proposed here to improve the accuracy of dispersiveFDTD scheme is realized by applying conformal technology at the interface between twoadjacent dispersive medium so as to depress the stair-casing error, which is resulted fromusing cubic cell to approximate the curved surface. Based on the improved dispersiveFDTD scheme, electromagnetic scattering of complex dispersion medium, includinghypersonic plasma sheath, invisibility cloak structure, and so on, has been investigatedsystematically. The major contributions of the thesis can be summarized as follows:1. The numerical errors of FDTD scheme have been studied. The numericaldispersion and dissipation errors resulting from the space and time differenceapproximation of FDTD scheme when modeling dispersive and non-dispersive mediumwas analyzed in detail, and the expression for numerical wavenumber of SO-FDTDscheme modeling dispersion medium has been deduced. Then, the influence of cell size,plasma frequency and collision frequency on the numerical dispersion and dissipationerrors of both SO-FDTD and PLRC-FDTD schemes when modeling uniform dispersivemedium has been investigated. Finally, a equivalent error model have been proposed toevaluate the errors from dispersive FDTD scheme, and the dispersion and dissipationerrors of PLRC-FDTD scheme when calculating the electromagnetic characteristic ofnon-uniform plasma medium have been studied based on the proposed model.2. The study of methods to improve the accuracy of FDTD scheme. A hybridFDTD(2,4) scheme for analyzing the three-dimensional electrically large scattering problems was proposed. Numerical results demonstrate that the proposed scheme wouldimprove the accuracy and save the computer resources significantly compared to theclassical FDTD scheme involved in the radar cross section (RCS) simulation. At the sametime, the FDTD(2,4) scheme has been introduced into SO-FDTD scheme to enhance theaccurate level when modeling dispersive medium. Moreover,a dispersive conformalFDTD method has been proposed to accurately model the interface between two adjacentdispersive mediums, and has been implemented to study the scattering of THzelectromagnetic waves of inhomogeneous collisional plasma cylinder array. The methodis based on the technology of area average, which is different from existing dispersiveconformal FDTD schemes. Numerical results show the proposed method would modifythe accuracy level compared to the stair-casing FDTD scheme involved in theinhomogeneous plasma.3. The study of electromagnetic propagation and scattering characteristic of thereentry plasma sheath. The stability condition of PLRC-FDTD and SO-FDTD schemehas been derived, the stability of the two schemes in the cases of different incidentelectromagnetic wave frequencies has been compared. Numerical results show that theSO-FDTD scheme is more suitable for modeling reentry plasma sheath. Thecharacteristics that the electromagnetic wave propagates in the reentry plasma sheath withdifferent plasma frequencies and collision frequencies have been compared. Based thedifferent flying scenes, the influence of reentry plasma sheath on radar targetcharacteristics have been computed and analyzed contrastively.4. The study of electromagnetic scattering of simplified cloaking structure. Due tothe permittivity and permeability of the cloaking structure are space-varying, dispersiveand anisotropic, a SO-FDTD(2,4) scheme has been proposed to accurately modelcloaking structures. The exotic electromagnetic parameters of the cloaks are taken intoaccount using shift operator based on dispersive FDTD method. The introduction of thehigher-order algorithm would reduce the numerical dispersion of the FDTD method andguarantee a coarser grid during the simulation. Numerical results have indicated that theproposed method is more accurate than the available method maintaining the same gridsize. Electromagnetic scattering characteristic of different kinds of simplified cylindricalcloaks including thickness and loss is presented.
Keywords/Search Tags:Plasma sheath, Metamaterials, Electromagnetic Scattering, Finite-difference time-domain method, Radar target characteristic
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