CST – Computer Simulation Technology

Shielding Analysis of a Metallic Enclosure

The prediction of the shielding performances of metallic enclosures used for telecommunication devices is an important part of the global design process. The desire for a reduced time-to-market means that there is often no time or budget for performing extensive prototyping and test measurements. These limitations make the reliable computation and prediction of the shielding properties of a given structure critical. The CST MICROWAVE STUDIO® (CST MWS) Transient solver was used for the simulations which provides time and broadband frequency data from a single simulation.

Figure 1: CST MWS model geometry.

The shielding properties of an actual metallic rack have been simulated with CST MICROWAVE STUDIO® (CST MWS). Figure 1 shows a view of the CST MWS model of the metallic rack. A plane wave is used to illuminate the rack with monitor probes defined inside the rack  for recording the electric field  in order to allow the shielding effectiveness (SE) to be evaluated....

Figure 2 shows a photograph of the designed rack as well as the experimental set-up.

Figure 2: Photograph of the metallic rack and experimental setup.

Figure 3: S11 and S21 comparison between measurements and CST MWS simulations

The equivalent electromagnetic model was validated by means of measurements of S-parameters  as shown in Figure 3 .  Excellent correlation between simulation results and measurement can be seen.

Figure 4: CST MWS 3D equivalent electromagnetic models

A sensitivity analysis on SEy is then performed and 4 cases are studied:

1) The enclosure is perfectly closed but with the connector holes open.

2) The cover is screwed on and the connectors metallically closed

3)  The same configuration as in case 2, but with a dielectric material introduced between the cover and the walls to represent the presence of the gasket

4) The enclosure has a floating cover placed at a distance of  0.1mm from the lateral walls.  All connectors are metallically closed  as shown in Figure 4.


The Shielding effectiveness (SE) frequency spectra results are presented in Figure 5.

Figure 5: SEx and SEy spectra

In this article the effect of various geometries and configurations on the shielding effectiveness of a metallic enclosure was investigated.  The validation of the numerical model used for the SE computation is demonstrated by comparing the results of the CST MWS Transient solver simulations with experimental results. Excellent  agreement could be seen in the comparison. The Transient solver is dieal for such simulation since it provides broadband frequency results in just one simulation. In addition, the time domain variation of fiueld quantities can also be extracted from the simulation.



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