An Electromagnetic Topology Theory-Based Research On Shielding Performance Analysis Methods Of Enclosures

Electromagnetic shielding is a significant measure in electromagnetic interference(EMI) control and also a preferred design method in electromagnetic compatibility(EMC). Shielding enclosure can decrease the damage of EMI effectively; it influences the EMC of equipment closely. Consequently, research on shielding performance analysis methods of enclosures is of great value. Recently, Electromagnetic Topology Theory(EMT) has been employed in analyzing shielding performance of enclosures. This dissertation studied on shielding performance analysis methods of enclosures based on EMT, expanded the application scope of EMT and BLT(Baum-Tesche-Liu) equation in shielding analysis and design. Three main aspects in this dissertation are included as follows(1) Study on shielding effectiveness calculation method of enclosures based on BLT equation. The shielding effectiveness calculation method of enclosures based on BLT equation was extended further Firstly, generalized BLT equation containing the properties of interference source and aperture was established by means of building equivalent model and calculating the scattering parameter of apertures. The shielding effectiveness of the center line of enclosures can be figured out through generalized BLT Equivalent circuit method and simulation tested the validity of the proposed method. Then, generalized BLT was extended to calculate the shielding effectiveness of double layer enclosures. Based on the waveguide theory, the correlativity between electric field of arbitrary observation point and electric field of center line was obtained. Finally, the formula of shielding effectiveness of arbitrary observation point in enclosures was deduced. And the formula was tested later.(2) Study on EMI calculation method of transmission line load enclosed in enclosures based on EMT. Based on EMT and good shielding approximation, the course of outer interference source radiating transmission line enclosed in enclosures was decomposed into two relative independent sub problems. Low frequency approximation theory was employed to calculate the inner electric field of enclosure irradiated by the plane wave. Then, the electric field obtained was regarded as the excitation source of the transmission line. Agrawal’s model was used to deduce the voltage BLT equation and the load interference voltage can be figured out through the equation. The method proposed was verified by numerical method, and the applicability was studied deeply.(3) Study on EMI calculation method of nested enclosures based on EMT. The integrated electromagnetic response analysis method of nested enclosures based on EMT was studied. By establishing the EMT model of nested enclosures, all the interference transfer paths of system were analyzed and the main interference path was ascertained. Analytical method and numerical method were employed to calculate the main interference path, respectively. There were many assumptions and approximation within analytical method, so it could handle less model and the calculation error was biggish. But the calculation time of analytical method is much short. Hybrid method could obtain precise electromagnetic response, and it could work out many actual engineering problems. The computing resource of hybrid method was a little bit more than analytical method, but its time is much less than numerical method.