Towards accurate time-domain simulation of highly conductive materials

Accurate simulation of highly conductive materials such as copper at RF and microwave frequency has presented a great challenge with the conventional FDTD method. The reason is that for a FDTD recursive computation to be accurate and stable, the FDTD time step has to be very small, leading to sometimes a prohibitively large number of iterations. In this paper, the recently developed unconditionally stable ADI-FDTD method is revised and applied to solve the problem. It is shown, through the examples of computation of body of rotational (BOR) cavities with highly conductive walls, that the highly conductive materials can now be accurately simulated. In addition, a general unconditionally stable cylindrical ADI-FDTD formulation is developed to facilitate the computation of cylindrical structures with conductive loss.

I. Introduction

The FDTD of Yee's scheme has been widely used to solve various electromagnetic problems [1]. In theory, it can be applied to compute arbitrary media including highly conductive materials. In practice, however, due to the CFL stability condition and numerical dispersion, the time step for a FDTD mesh in a highly conductive region becomes so small at RF and microwave frequencies that the number of iteration becomes prohibitively huge. As a result, approximating approaches, such as Surface Impedance Boundary Condition (SIBC) and perturbation techniques, were developed with the assumption of plane waves impinging on the conducting boundaries or unperturbed fields in the unperturbed regions [2]. These methods, though presenting good results in many cases, remain to be of approximations in nature and fail in some special cases.