Shielding Effectiveness Analysis Of Small Geometry Rectangular Metallic Enclosure

With the miniaturization and highly integration of electronic devices, a qualifiedelectronic product must meet the requirements of EMC standards. Shielding is one ofimportant methods in electromagnetic compatibility design, modules in the electronicsystem require to be shielded in small metallic cavity, in order to protect the internalcircuit. Although an ideal rectangular metallic box with no apertures can provide goodshielding capability, but in fact, a rectangular box must be punched in the panel, and theseapertures provide a coupling path between internal and external energy, which has a greatimpact on the stability of working equipments. Therefore, it’s very necessary to calculate,measure and simulate shielding effectiveness of small rectangular cavity.In this paper, the definition of shielding effectiveness, analytical calculation methodsof the ideal rectangular metal cavity and the rectangular cavity with holes have beenintroduced, and principles, feasibility, merits and drawbacks of shielding effectivenessmeasurement and electromagnetic compatibility test sites have been analyzed. Accordingto the requirements of practical engineering application, a small rectangular metalshielding cavity has been designed, a test plan for shielding effectiveness of the smallrectangular metal cavity has been proposed, and the shielding effectiveness of thedesigned cavity has been measured. A simplified model and a modified model of therectangular metal cavity have been established in CST MWS. Comparing results oftheoretical analysis, experimental measurement, and modeling and simulation, aconclusion can be drawn: the resonant frequency of the transmission-line equivalentcircuit model is very close to the frequency of the simplified cavity model, and themeasurement result of shielding effectiveness of the cavity is in coincidence withshielding effectiveness curve of the modified cavity model. This conclusion fullydemonstrates the reliability of the analytical methods used herein, which provides animportant reference to the analysis of the small rectangular metal cavity.