CST – Computer Simulation Technology

Cavity Modes in a Shielding Enclosure

Ms. Lis box: This shielding enclosure shows electromagnetic interference (EMI) from a slot, caused by the coupling of the internal source with cavity modes. Measured results have been compared with a FDTD calculation by M. Li, J. Nuebel, J.L. Drewniak, R.E. DuBroff, T.H. Hubing and T.P. Van Doren in: \"EMI from Cavity Modes of Shielding Enclosures - FDTD Modeling and Measurements\", IEEE Trans. on Electromagnetic Compatibility, 42, 1, Feb. 2000.

This topic is of particular interest in the field of high-speed digital design because the effectiveness of shielding enclosures is reduced by apertures for heat dissipation, cable penetrations, CD ROM slots and other openings. The authors demonstrated the usefulness of finite-difference time-domain (FDTD) for the calculation of these problems. We recalculated the structure with CST MICROWAVE STUDIO® (CST MWS) and got excellent results. Thanks to perfect boundary approximation (PBA), just a few mesh points are needed for the modeling of the coaxial conductor and the slot....



Figure 1: Shielding enclosure


Figure 2: Publication and MWS result

Delivered Power: measured (black line) and calculated (black dotted line), by Li et al., and calculated with CST MWS. Good results can be achieved using a coarse grid with 28,000 nodes within 9 minutes (green line). If the accuracy requirements are higher, excellent results can be achieved using a finer grid within 35 minutes (red line). In both cases an auto regressive filter function (AR filter) has been used in order to reduce the necessary calculation time. The CST MWS calculation has been performed on a Pentium II processor with 400 MHz clock rate. The files used for the calculations can be sent to CST customers on request.



Figure 3: Eletric field im 3m

Li et al. also calculated (dotted black line) and measured (black line) the electric field strength 3m away from the shielding cavity. Again the CST MWS results show very good agreement. CST would like to thank Dr. Caniggia at ITALTEL, Milano, for providing these results. The Italian telecommunication provider uses CST MWS for EMC problems.

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