Analysis Of The Shielding Effectiveness With Incident Wave Of Arbitrary Polarization Angle

In the electromagnetic compatibility (EMC) design to equipment and system, metallic conductor is widely used to shield from electromagnetic interference (EMI), and shielding is a main technique. To most electronic equipment, it is hard to meet the requirement of EMC without shielding measurement. However, due to the various needs such as input and output connections, ventilation panels, etc, there are apertures or slots on the conducting shield inevitably. These apertures or slots are the main factor to influence the shielding performance of system. So, to EMC forecasting and design of the electronic devices and system, it will be of high practical significance to understand the mechanism of electromagnetic scattering, transmitting and coupling through the apertures on the metallic shield.In this paper, the shielding technique of metallic cavity is discussed in the field of EMC, and the effects of incident electromagnetic plane wave with arbitrary polarization angle on the shielding effectiveness of a rectangular metallic enclosure with aperture is specifically studied. Both Transmission Line Method based on analytical method and Finite Element Method based on numerical method are involved, with the consideration of the single transmission mode and multiple transmission mode.Firstly, by utilizing the Transmission Line Method, the model is transformed to transmission line circuit equivalently, then electric field and magnetic field is equalized to voltage and current in the circuit model, consequently the shielding effectiveness is concluded by voltage and current. As for the incident plane wave with arbitrary polarization angle, the electric field is decomposed into two orthogonal components, after each components being analyzed in terms of Transmission Line Method respectively, the final shielding effectiveness is obtained by combine the two components. For multiple mode co-existing situation, based on the analysis above, by combining the result of each components calculated under multiple transmission mode, the formula of the shielding effectiveness is conducted finally.Then, by utilizing the simulation software HFSS based on Finite Element Method, after a series of work such as modeling, parameter setting, meshing, result setting and iterative calculation, the simulation of the shielding effectives is realized.Finally, under the situation of single transmission mode and multiple transmission mode, by analyzing the results of the two methods with different polarization angle respectively, the relationship between the shielding effectiveness and the polarization angle of the incident wave is obtained successfully. By comparing the results of the two methods, the validity of the Transmission Line Method is verified.