Investigations On The Electromagnetic Imaging Techniques Based On FDTD Numerical Simulation

Electromagnetic imaging is an important aspect of the application about electromagnetic inverse scattering theory, and it is to reconstruct the shape or the dielectric constant of the unknown scatter from the incident field and the scattering data measured outside. The electromagnetic imaging techniques have received considerable attention in the past few years, as they can be suitable for a number of important applications such as medical science, nondestructive detection and so on. There are a lot of questions worthy of more research in the field of electromagnetic imaging, and the electromagnetic imaging problems can be studied from different point of view. According to the type of incident waves and the complexity of the scattering problem this article focused on two-dimensional TM wave imaging.The imaging problem can be divided into two parts, a direct or scattering problem and inverse problem, and the scattering problem which can be solved by several numerical methods. This paper mainly introduced the basic principle of Finite- Difference-Time-Domain(FDTD), and the two-dimensional FDTD equations is derived from Maxwell's equations, and simulated as well as at different boundary conditions by setting up suitable excitation source, grid size, the space and time step.To solve the inverse problem, several optimizing methods can be used, such as based on the gradient method, etc. The electromagnetic inverse scattering is one of most difficult problem due partly to its ill-posed, nonlinear and instability nature. In this paper, we combined the physical model of inverse scattering problem and neglected multiple scattering within the objects. meanwhile, linear optimization technique based on Born approximation and the Rytov approximation is usually used to solve the weak scattering problem. The results of the calculation is not right if the sick do not be a better deal which is due to the error is inevitable in the process of electromagnetic imaging. In this paper, Tikhonov's regularization method is used to improve the ill- posed of inverse scattering problem, and then improve the stability of solution. One of an important question about electromagnetic imaging is to reconstruct the shape or the electromagnetic parameters. In this paper, Gel'fand-Levitan equation reconstruction algorithm is adopted to the one-dimensional problem. This paper studied the Fourier diffraction imaging about the reconstruction of two-dimensional medium objective, and focus on the two-dimensional cylindrical target.Finally, this paper bring about the simulation of square cylinder, cylinder and heterogeneous media at TM wave incident circumstances by setting up suitable grid size, space and time step as well as the Mur and PML boundary conditions, make analysis and interpretation at last.