Simulation of the Shielding Eeectiveness of Cabinets Used in Communications Equipment I Introduction Ii Brief Introduction to Tlm

The basic formulations used in the description of thin walls and small apertures in simulations based on the Transmission-Line Modelling (TLM) method are described. It is shown that eecient and accurate methods are available which exhibit a reasonable balance between accuracy and computational eeciency. Results of simulations are presented showing the shielding eeectiveness of cabinets. Of all aspects of design innuencing the electromagnetic compatibility (EMC) of equipment, electromagnetic shielding is the one in which the EMC designer has the maximum degree of control. EMC problems occur because a source of electromagnetic interference (EMI) affects , through coupling paths, the operation of an electronic system (the victim of EMI). The EMC designer has little control on externally generated interference and limited input in the design of the potential victim system which is dominated by operational considerations 1]. Good shielding on the other hand can remove or diminish coupling paths and thus unsure EMC. However, shielding adds cost, weight, interferes with access and cooling and may be aesthetically unacceptable. It is, therefore, imperative to be able to predict the performance of shielding arrangements in complex systems. Modern predictive design tools are computer-based. Hence, this paper deals with such tools based on the Transmission-Line Modelling (TLM) method 2]. TLM is a time-domain, diierential method ooering a degree of generality and versatility which is essential in EMC simulations. One aspect of this approach, however, which can cause diiculties, is the description of ne features in an otherwise large problem space. Typical situations where this occurs are in the description of ne slots, joints and thin walls, regularly found in practical equipment cabinets and shields. While, in principle, it is possible to use a very ne mesh around speciic ne features only and thus economise on computer resources, the diierences in physical scale are normally so large as to make this approach unprootable. In many practical problems it has been found necessary to devise special formulations, which are outside a full three-dimensional eld solution, which give an accurate description of ne features at a fraction of the computational cost of a full eld solution. Two speciic problems are described here. First, the modelling of thin panels made our of poor electrical conductivity materials is presented. Second, the manner in which EM wave penetration through small holes may be described in the TLM model, using the equivalence principle, are presented. Applications of the model in the …