Evaluating tools which predict the shielding effectiveness of metal enclosures using a set of proposed standard EMI modeling problems

Numerical modeling tools are becoming very popular for a variety of EMI/EMC applications. Metal shields around printed circuit boards remain one of the primary techniques used to control emissions and provide immunity. Predicting the shielding effectiveness of these metal shields is complex, but certain full wave modeling techniques can be used to predict the shielding performance, for both near-field and far-field emissions. Not all numerical modeling techniques are equal. Every technique has strengths, that is, certain types of applications where it excels, as well as weakness where it can not efficiently perform the modeling necessary. The method of moments (MoM) and the finite-different time-domain (FDTD) technique are the two most commonly used modeling techniques for EMC shielding applications. This paper presents the results of modeling the same shielding configurations with a number of different modeling tools, using both MoM and FDTD, and demonstrates the limitations of these techniques against this application. Since shielding effectiveness is very dependent upon the actual test/model configuration, a set of standard shielded enclosures is proposed and then each is evaluated using each of the modeling techniques. Two different size enclosures are included, and each with two different size apertures. The enclosures were also modeled without apertures to show the dynamic range limitation of both modeling techniques