Research On Inversion And Image Method For3-dimensional Objects In Multilayered Media

Developing the electromagnetic (EM) inverse scattering and image methods toreconstruct objects buried in multilayered media is significant. It can be applied ingeophysical exploration and through-wall radar detection.The two-dimensional problemis proposed and developed since1980s. It is not as suitable as three-dimensionalinpractical application. So the numerical analysis for scattering and reconstruction of3Dtargets in multilayered media is an important field. But it is not an easy task to solve theintegral equation and study key techniques for3D scattering problems in multilayeredmedia. Therefore it’s full of challenge to study the inverse problem. This thesis willstudy a fast algorithm for3D multilayered media inverse problem. The inversion resultis based on simulation data.The main contribution of this dissertation is list as follows.1. The computation method for EM scattering is the basis of research on imagingand inversion method. For different inverse method, we use the volume integralequation (VIE) method or FDTD to calculate the scattering field. FDTD is simplydescribed. We derive the dyadic Green’s function (GF) in details and study theSommerfeld integral for GF in VIE. They’re the key techniques for VIE. Theconventional method of moments (MOM) is limited to small-scale models. We willcombine a fast solver to develop for large-scale EM scattering from inhomogeneousobjects in a planarly multilayered media. The biconjugate gradient stabilized (BCGS)with fast Fourier transform (FFT) method is an accurate and efficient solver forelectric-field integral equation (EFIE).2.Reconstruct and image dielectric objects by using the Born iterative method(BIM), distorted Born iterative method (DBIM) and metal objects by using TimeReverasal Mirror（TRM）technique. To process the ill-posed problem, this dissertationinvolves Tikhonov regularization method. And the choice of regularization parameter isvery important. If it is too large the iteration may converge slowly, if it is too small thesolution may not converge. We have an example to compare DBIM and BIM, finallyDBIM is applied in the inverse and image.3.TRM is used to reconstruct the metal objects in multilayered media. Through changing the polarization, the metal which is put along the polarization direction canform a clear image.The result combining the images of different sources excite byorthogonal polarization can react the actual objects.The research presented in this dissertation provides an efficient way to reconstructthe dielectric or metal objects in the multilayer media. It is a solid foundation for thefuture research.