Invited PaperNumerical Calculation Of Magnetic Shielding Effectiveness OfEnclosures Using The Frequency-domain TLM Technique

Abstract

The ability to predict the electromagnetic shielding afforded by electronic equipment housing is important in designing to satisfy the Electromagnetic Compatibility (EMC) directives introduced recently. Electromagnetic energy can penetrate into the housing by coupling through apertures in the housing surface, diffusion through the walls of the housing and by conduction of current along wires. The shielding effectiveness of the housing is dependent on both the shape of the housing and the electrical properties of the housing material. 3-D numerical modelling enables the design engineer to consider a wide range of housing shape and material permutations in the early stages of design, which can save time and costs associated with developing prototypes and evaluating their susceptibility and emission characteristics by tests. Transmission-Line Modelling (TLM) is a well established time-domain method which has been developed for the simulation of 3-D electromagnetic problems [1]. TLM has been applied to EMC analysis and recent work has shown good agreement in comparisons with measurements [2]. To compliment the time-domain TLM method, a new frequency-domain TLM method has been developed recently [3,4]. The frequency-domain approach can offer a significant saving in computation time for finding steady-state solutions to certain classes of problems. There have been many developments in time-domain TLM to tailor the general 3-D algorithm specifically to EMC problems. These include special models for thin wiring [5], narrow slot apertures [6] and thin lossy panels [7] which despite their small dimensions may have a large effect on the electromagnetic field. This paper deals with the application of frequency-domain TLM to EMC problems. In particular, we use frequency-domain TLM to calculate the magnetic shielding-effectiveness (MSE) of different kinds of enclosures. First of all, we describe the 3-D electromagnetic modelling software which has been developed to provide a user-friendly implementation of the TLM algorithms.