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FDTD Method Applied To The Transient Electromagnetic Enqineering

Posted on:2001-06-10Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y B YanFull Text:PDF
GTID:1118360002451298Subject:Electromagnetic field and microwave technology
Abstract/Summary:PDF Full Text Request
Transient electromagnetic analysis is widely applied in many electronic engineering areas. In this dissertation, Transient electromagnetic scattering from objects are studied by using the Fiite-Diffa~ence Time-Domain (FDTD) method. The following problems are considered: the wide-band scattering from complicated objects in free space, the time- domain surface current of a cable above a lossy ground, and transient scattering from barred targets in lossy ground. And also, we present a hybrid STF-FDTD approach to compute the EM scattering with an extremely slow-decaying pulse incidence. Firstly, we study the wide-band EM scattering from a target of complicated geometrical shape or material composition in free space. A scheme for modeling a complicated object for FDTD computation is presented. Making up the descriptive file for the objects, we can obtain the discretized EM model using this algorithm. The EM scattering from an airplane is then analyzed within frequency range 3-15MHz based on the above object modeling. These studies found their practical values in the beyond-horizon radar detection areas. Next, we analyze the transient EM scattering of an airfoil and a lip of an inlet and their RCS reductions by partially RAM coating or filling. In all the above analysis, pulse incidences are used in the FDTD calculations and the transient scattering fields are computed. We can transfer these time-domain results into frequency-domain with the help of Fast Fourier Transform (FFT). Secondly, the transient EM scattering analysis of targets above a lossy ground is proceeded. Surface impedance is introduced into the FDTD method. Based on the Fresnel reflective coefficient and Laplace Transform, we derive the time-domain Surface Impedance Bouixlary Condition (SIBC) available for the FDTD method. The lossy ground is then replaced by this time-domain SIBC, reducing the solution space and producing significant computational savings. By using this approach, we study the problem of. EM pulse coupling into a cable above a lossy ground. Next, we enhance the FDTD method for simulating transient EM surveys for underground objects, in which a step or impulse excitation is laid on the ground surface and the electromotive force (EMF) is measured along the ground surface. Normally the transmission of the electromagnetic fields in lossy medium is characterized with wavelike and diffusive features. In the condition that conductivity a is much large and permittivity s much small, the wavelike feature vanishes very quickly (and it is difficult to simulate in 桰l? the numerical methods), leaving only difftmive behavior. Thus the fields under ground satisfy the diffusion equation. By comparison of the Green抯 function of damped wave equation and diffusion equation, we introduce an artificial displacement current term in the diffusion equation, which leads to the DuFort-Frankel method and FDTD method in the transient scattering analysis for underground targets. Finally, we present a hybrid approach of scattering t.raisfer function (5Th) and finite difference time domain (FDTD) for the calculation of electromagnetic transient responses when the incident wave is an extremely slow-de醓ying pulse, e.g., double-exponential pulse. First, we introduce the scattering transfer function (STF) concept into the scattering system based on the principle of the linear system theory, by using a fast-decaying pulse as an incident wave with the bandwidth of interest. Next, we derive the scattering respon...
Keywords/Search Tags:Transient Electromagnetics, Finite-Difference Time-Domain (FDTD) Method, Object Modeling, Radar Cross Section (RCS), Surface Impedance Boundary Condition (SIBC), DuFort-Frankel Method, Scattering Transfer Function (STF)
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