The Research and Application of a Novel Time Domain Hybrid Method for EMI Analysis of Lumped Circuits in a Shielded Device

This paper presents a novel time domain hybrid method consisting of finite-difference time domain (FDTD) method, transmission line (TL) equations, and circuit-based method, which can be directly applied in time domain for the electromagnetic interference (EMI) analysis of the lumped circuits in a shielded device excited by ambient electromagnetic wave. The FDTD method coupled with the TL equations is utilized to model the electromagnetic properties of arbitrary structures containing transmission lines and shielded enclosure of the electronic device with any ambient excitation. With numerical simulation, an equivalent circuit model considering the external EMI effects is extracted as an excitation source for the internal lumped circuit according to Thevenin's theorem. Then, the state variable approach is used for the further EMI analysis of the internal lumped circuit in time domain. Two cases, in which a transmission line and/or a transmission line network are connected to a lumped circuit within a shielded enclosure excited by an intense electromagnetic pulse, are computed with the proposed method. The numerical results are compared with those obtained by using the FDTD method, and they are almost in perfect agreements. Meanwhile, at last, an example of this method applied for the EMI protection of an electronic device is given.