Imaging Of Perfectly Magnetic Conducting Rough Surface Through Single Frequency Single View Data

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2008Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2008Bu çalışmada, manyetik iletkenlik özelliğine sahip bir yüzeye ait ters problem çözümü sunularak, cismin şeklinin ve elektriksel özelliklerinin bulunması için yeni ve hızlı bir metot verilmiştir. Öngörülen sistemde, yüzeyden saçılan elektromanyetik dalgalar yüzeyden yukarıda bir düzlem boyunca ölçülür. Kullandığımız yöntemde ölçün yapılan uzayla, bulunması hedeflenen yüzeyin arası varsayımsal bir düzlemle iki yarım uzaya bölünür. Üst kısımda kalan her noktadaki saçılma, Fourier transformu ifadesiyle tanımlanır. Daha sonra manyetik iletkenlik özelliğine sahip bir yüzeydeki sınır koşulları kullanılarak problem lineer olmayan bir denkleme indirgenirThe main aim of this thesis is to give a new, simple and fast method to determine the location and shape of a perfectly magnetic conducting rough surface. The surface is reconstructed using the illumination by a single plane monochromatic wave and the near field measurements of the scattered field are performed on a line parallel to the mean surface. The novelty of the method is that the lossy half-space above the surface is first separated into two parts by an estimated plane, and then the scattered field in the upper region above this plane is expressed in terms of a Fourier transform while it is expanded into a Taylor series in the lower part. The boundary condition on the Perfect Magnetic Conductive surface requires that the normal derivative of the total electric field should vanish. The use of this condition allows the reduction of the problem to the solution of a non-linear equation for the unknown surface function.Yüksek LisansM.Sc

FURTHER INVESTIGATION ON MAGNETICALLY INDUCED SUBSEQUENT FAULT AND STUDY ON ELECTROMAGNETIC SCATTERING OF OBJECTS BURIED BELOW A RANDOM ROUGH SURFACE

This dissertation contains two subjects: further development of numerical technique for the analysis of magnetically induced subsequent fault (MISFault) in overhead power lines and its implementation into a software upgrade; and first-phase of study on the electromagnetic scattering from objects buried below a random rough surface making use of the multidomain pseudospectral time domain (PSTD) method and Monte-Carlo simulation. An initial electric fault can result in strong magnetic torque on the overhead power line conductors, which will make them swing and may bring them to close proximity or in contact with one another, causing a subsequent fault. In Chapter 2, Computer simulations for the analysis of the subsequent fault in transition spans, which are often required in power line topology, are developed. A dynamic analysis of swing movement of power line conductors subsequent to an initial fault is presented to track the smallest distance between the conductors. In Chapter 3, the simulation is implemented into the upgrade of the MISFault analysis software. Its functions are depicted in details. The MISFault software is being used by Duke Energy Company and is expected to be useful to a utility for eliminating the magnetically induced subsequent faults. The multidomain pseudospectral time domain (PSTD) method has been developed and successfully applied to solve a variety of electromagnetic scattering problems in the past decade. It is a novel algorithm with improvement over traditional FDTD method. In Chapter 4, a multidomain PSTD algorithm is developed to investigate the scattering from a 2-D cylinder in free space. Sample numerical results are presented and validated. Then, the theoretical derivations are extended for the analysis of scattering from 2-D objects buried below a random rough surface

Study on Electromagnetic Scattering of Cylinders Buried in a Half Space with Random Rough Surfaces of Finite/Infinite Length

Analysis of electromagnetic scattering of buried objects is a subject of great interest due to its practical importance in both military and civil applications, such as subsurface investigation and target detection. In reality, the earth is of layered structure of random rough interfaces, which leads to a greatly increased complexity of the analysis. However, it is necessary to incorporate the nature of random rough surface and the layered structure because they both have substantial impact on the scattered signature and hence affect the study of inverse scattering and detection of buried objects. In this dissertation, a Monte-Carlo multidomain pseudospectral time domain (MPSTD) method is developed for investigating the scattering from cylinders buried below a random rough surface separating two half spaces under various conditions. As a prelude, the formulation of multidomain PSTD algorithm is presented. Then, this formulation is extended and combined with the Monte-Carlo approach to analyze the scattering of an object buried below a random rough surface of finite length. In the analysis, special attention is paid to the treatments of the random rough surface including its profile generation, matching with CGL points, and subdomain patching. Next, the scattering of a cylinder buried below a random rough surface of infinite length is studied and a two-step computation model based on the Monte-Carlo MPSTD method is developed. Further, in order to better simulate the real situation, the analysis is then extended to study the scattering from one or more cylinders embedded in a layered half space with random rough surfaces. Finally, a near-zone field to far-zone field transformation technique is developed and presented. Sample numerical results under different conditions, involving random rough surface of various roughness, lower half space with different permittivities, and cylinders of circular and rectangular shapes are presented, validated, and analyzed. Throughout this research, a numerical technique based on Monte-Carlo method and MPSTD approach has been developed and validated for investigating cylinders buried in a half space with random rough surfaces. It is observed that the roughness of the random rough surface and the electromagnetic properties of the lower half space can significantly affect the scattered signature of the buried object