Numerical simulation using ADI-FDTD method to estimate shielding effectiveness of thin conductive enclosures

Numerical simulations were run using the alternating-direction implicit-finite-difference time-domain (ADI-FDTD) method to calculate the shielding effectiveness of various enclosures. The enclosures were composed of very thin conductive sheets, which are generally fabricated using conductive paints or electroless plating techniques on plastic surfaces. In this case, very fine cells must be used for finite-difference time-domain (FDTD) modeling. In the conventional FDTD method, fine cells reduce the time-step size because of the Courant-Friedrich-Levy (CFL) stability condition, which results in an increase in computational effort, such as the central processing unit (CPU) time. In the ADT-FDTD method, on the other hand, a larger time-step size than allowed by the CFL stability condition limitation can be set because the algorithm of this method is unconditionally stable. Consequently, an increase in computational efforts caused by fine cells can be prevented. The results from the ADI-FDTD method were compared with results from the conventional FDTD method, analytical solutions, and experimental data. These results clearly agree quite well, and the required CPU time for the ADI-FDTD method can be much shorter than that for the FDTD method.

I. Introduction

IN RECENT years, it has become increasingly important to estimate the electromagnetic shielding effectiveness (SE) of the cases that enclose various types of electronic equipment. For optimal cost efficiency, using a numerical technique during the design phase of the equipment is indispensable for estimating the SE of various shapes and materials for these enclosures. The finite-difference time-domain (FDTD) method [1] is well known as being one of the most useful numerical techniques for such problems. However, for calculating the effectiveness of an enclosure whose thickness is much smaller than the operating wavelength, the conventional FDTD method has a disadvantage. For the FDTD modeling, very fine cells must be used in the region with thin sheets, and these fine cells reduce the time-step size because of the Courant–Friedrich–Levy (CFL) stability condition [2], which results in an increase in computational effort, such as the CPU time. In fact, several micrometer-thick thin shielding sheets, which are generally fabricated using conductive paints or electroless plating techniques on plastic surfaces, are often used today, thus, the inefficiency of the FDTD method is a very serious issue for optimizing the design process.