Electromagnetic Imaging Of Dielectric Rough Interfaces

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2008Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2008Bu çalışmada, engebeli dielektrik arayüzlerin elektromanyetik görüntülenmesi üzerinde çalışılmıştır. Konu iki bölümde ele alınmıştır: İlk olarak mükemmel iletken düzlem üzerindeki dielektrik yüzeyin elde edilmesi problemi incelenmiştir, ikinci olarak ise üzerinde dielektrik katmanlar bulunan dielektrik yüzeyin elde edilmesi problemi aynı metot ile incelenmiştir. Tek boyutta değişimlerin olduğu yüzeylerin sabit frekanslı düzlemsel dalgalar tarafından aydınlatıldığı durum göz önüne alınmıştır. Hesaplanacak yüzeyin üzerinde kalan bölgede ve yüzeye paralel bir çizgi üzerindeki saçılan alan ölçümleri problemin çözümünde kullanılacaktır. Saçılan alan Fourier Dönüşümü ve Taylor Açılımı ile ifade edilir; problemin çözümü sınır koşulları kullanılarak elde edilen lineer olmayan denklem sisteminin çözümüne indirgenir. Denklem sisteminin çözümünde ise Newton Metodu yinelemeli bir şekilde uygulanırken regularizasyon uygulanmasını gerektirir. Bu çalışmada Tikhonov Regularizasyonu uygulanmıştır. Ayrıca, daha doğru sonuçlar elde edilmesi için kimi durumlarda En Küçük Kareler Yöntemi kullanılmıştır. Benzetim sonuçları, problemde kullanılan parametrelerin etkisine bağlı olarak incelenmiştir. Sonuç olarak iki problem için de dalgaboyu/200 genlikli hasarların bile tespit edilebildiği gösterilmiştir ve kullanılan metodun; ters saçılım problemlerinde önemli bir konu olan ve çok geniş kapsamlı pratik uygulamalara sahip tahribatsız muayene için etkili olduğu gösterilmiştir.In this study, electromagnetic imaging of dielectric rough interfaces is presented with simulation results. The subject is presented in two cases: First, dielectric rough surface located over a perfectly conducting plane is reconstructed and second, dielectric surface beyond a layered media is reconstructed using the same method. Considering surfaces having variation only in one space dimension, plane electromagnetic wave with a fixed frequency is used for excitation. Scattered field measurements on a paralel line above the surface to be reconstructed are used and a special representation of the scattered field in terms of Fourier Transform and Taylor expansion is used in boundary conditions which leads to the solution of a system of nonlinear equations where Newton Method is applied iteratively with some kind of regularization. In this study, Tikhonov regularization is applied. In addition, in some cases, least square regularization is applied in order to get more accurate results. The simulation results are discussed with the effects of parameters used in the problems. Finally it can be shown that, satisfactory results are obtained in reconstructing the defects on the surfaces with the amplitude of wavelength/200 in both problems and the method can be effectively used in non-destructive testing of materials which is an important subject in the inverse scattering theory with its wide range of practical applications.Yüksek LisansM.Sc

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