A new approach for metallic boundaries formulation in TLM

Summary form only given. The TLM method is a time domain algorithm used for solving a great variety of electromagnetic wave-propagation problems. A typical problem in electromagnetic modeling is how to achieve an accurate description of the behavior of loss structures, such as good but imperfect conductor walls, while keeping within reasonable limits the use of computer resources. This paper presents a new way of using the surface impedance concept in the TLM method to model more easily, accurate and efficient loss conductor boundaries. The presence of an imperfect conductor material loss conductor boundary-is taken into account using the surface impedance concept. The values of this impedance-frequency dependents-are approximated by the values of a function in j/spl omega/, estimated from several values of surface impedance, which are analytically computed. The new proposed function to approximate the values of the surface impedance, is a ratio of polynomials with real coefficients. This function is used to compute the reflection coefficient that must be imposed in the mesh lines cut by a boundary, as a result of the presence of the conductor boundary. For the TLM algorithm this reflection coefficient is the analog model of the loss conductor boundary. This is transformed in the TLM model-discrete model-using bilinear transformation. Thus, the spatial quantification of the conductor wall, necessary in the TLM Green function concept in order to model the wave penetration in imperfect conductor material, is removed, allowing the use of large cells in the non-conducting region. The reflection coefficient of a plane wave incident on a copper wall has been computed with the new TLM formulation and compared with theory and the previous published results. The numerical simulations have confirmed the accuracy and efficiency of this new approach.