Study Of Method To Calculate Electrical Far Field From Openings In Shielding Enclosure

It is an important field of Electromagnetic Compatibility (EMC) subject to research the electromagnetic shield of electric device. Effective shield can prevent the electromagnetic Interference (EMI) from outside and reduce the radiation from the device itself. Because the shielding enclosure is compromised by opening(s) in side for heat dissipation, Input/Output (I/O) cable penetration, radiation from opening in enclosure excited by interior interferential source can vitiate the electromagnetic environment. Numerical modeling of electromagnetic field has been recognized to solve EMC of shielding enclosure at the beginning of design of product. This paper research the numerical simulation of the radiation from opening in shielding enclosure, and present a new method to calculate the far field which combines the Finite Difference Time Domain (FDTD) method and extrapolative Integral Equation (IE) based on the equivalent magnetic current on opening(s). This method can calculate the far field effectively, and the results determined by this method can give some advice to the electric product designer. The configuration of the problem become more complicate with the existence of some sorts of electric device, and the simulation must be a calculation of transient field because of the presence of source with pulse. FDTD method has outstanding advantage in these two aspect, so can be used for simulation of near field. It is problematic to directly determine the far field outside the metal enclosure by using FDTD method because of the necessity of modeling the entire interest space, both from the CPU and memory point of view. This is often circumvented by using the equivalent principle to determine the far field by equivalent currents generated in the near field simulated by FDTD method which is a solution of Integral Equation. This paper firstly builds up the extrapolation boundary by the conventional mode of null field equivalent current to determine the far field by formulation of time domain extrapolation, which is very mathematically complex, and the computational resource necessary to implement also can be substantial. This paper then deduce the IE based on the equivalent magnetic current on opening(s) which is approximated appropriately by Schelknuff's equivalent principle and image theory. It shows that this method allows the computer resource to be reduced. This paper builds some example of model with different openings. The agreement is quite good by the comparison with the results of directly FDTD simulation at a point near the opening and that of near-far extrapolation based on the null field equivalent current at a point far from the opening. The result calculated by this method also can be useful to the design EMC of the shielding enclosure.