| The enclosure structure is an important means to restrain electromagnetic interference and prevent electromagnetic leakage,being used to block the transmission of electromagnetic energy.However,due to ventilation cooling,fabrication and data transmission,the enclosure structure inevitably contains several types of electromagnetic coupling channels such as apertures,slots and cables,which impair the electromagnetic shielding effectiveness of enclosure.Therefore,in order to fast and accurately analyze the effect of the electromagnetic coupling channels on the shielding effectiveness of the enclosure,the equivalent modeling methods of the electromagnetic coupling channel and an analytic method for calculating the electromagnetic coupling on the enclosure are presented.The main research contents and innovations of this dissertation are as follows:(1)An equivalent modeling method of aperture array based on size effect of apertures is presented.Aperture is the most common back door electromagnetic coupling channel,and also an important way to cause electromagnetic interference.Numerous small apertures may lead to a huge number of grids in modeling the enclosure,especially in the analysis of electromagnetic characteristics of large complex enclosure,the simulation is formidable due to the presence of a large number of apertures in the enclosure.Thus this paper proposes an equivalent modeling method of aperture array,in which the aperture array is equivalent to a single aperture based on the condition that the field distribution in the enclosure is the same before and after the equivalent process.The proposed method can not only simplify the modeling process,reduce the number of grids,improve the efficiency of numerical simulation,but also can be used for the improvement of the Robinson model.The original Robinson model only linearly superimposes the impedance of each aperture,resulting in large deviation of the shielding effectiveness of enclosure with many small apertures.The proposed method in this paper can significantly improve the accuracy in the shielding effectiveness of the enclosure by Robinson model.(2)An equivalent modeling method for slots based on the theory of transfer impedance is proposed.Slot is another common back door electromagnetic coupling channel and the electromagnetic interference caused by the slot cannot be ignored.The large aspect ratio of slot causes a huge number of grids and consumes considerable computer resource in analyzing its electromagnetic compatibility.Thus,an equivalent modeling method for slots is presented to analyze the parameters of slots on the shielding effectiveness of the enclosure,in which the width of slot can be extend five times to balance the simulation time and accuracy.Finally,the conductive rubber filled at the slot and the loss medium filling inside the enclosure is devoted to suppress the electromagnetic coupling of the slot and enclosure resonance,which can establish a relatively clean electromagnetic space in the enclosure.(3)An equivalent modeling method of complex cable bundle based on load impedance is presented.The structure of the enclosure inevitably has power supply or signal transmission cables,which are considered as the common front door electromagnetic coupling channel.As the cross section size of cable is much smaller than the wavelength of the electromagnetic wave,we can use a lumped parameter circuit model to calculate the response on cable.However,the length of the cables is often similar to the wavelength of the electromagnetic wave propagating on the cable.In order to get a more accurate result,the electromagnetic theory is needed to analyze the cable.The "road" methods have certain limitations,and the "field" methods are too complex.To solve this problem,an equivalent modeling method of complex cable bundle from the "road" point of view is proposed,and then the "field" method is applied to calculate the simplified model of the cable in the numerical analysis.The simulation results show that the proposed method can significantly reduce the modeling process and improve the computational efficiency.(4)An analytic method based on Mode Matching technique and BLT Equation for the EMC characteristics of an enclosure is proposed.The aperture coupling and field-to-wire coupling are the typical issues of electromagnetic coupling calculation.In this chapter,an efficient approach is presented to calculate the electromagnetic coupling of a complex cable bundle in an enclosure,which involves two methods: mode matching and BLT equation.The issue is divided into the sub-problems: aperture coupling and field-to-wire coupling.The electromagnetic field in enclosure is calculated by the Mode function and Method of Moments,and the EMI of the cables in an enclosure is calculated by Agrawal's field-to-wire coupling theory and BLT equation.In comparison with measurement data shows that the electromagnetic field in enclosure can be accurately calculated by the mode matching method.The proposed method can also significantly reduce the simulation time and improve the efficiency of simulation compared with CST,which can be used to analyze the electromagnetic coupling of the enclosure.In this dissertation,the electromagnetic coupling channel equivalent modeling and calculation method of the enclosure structure can be applied to simulate and analyze the electromagnetic compatibility in the design stage of electronic products.Furthermore,the research achievements on analyzing the influence of the electromagnetic coupling channel structure parameters on electromagnetic compatibility,provide some reference and suggestions for the subsequent electromagnetic compatibility test and structure reform. |
PDF Full Text Request