FDTD Modeling of Thin Wires for Simulating Common-Mode Radiation from Structures with Attached Cables

The analysis of shielding enclosures is complicated by the existence of apertures and cables. The finite-difference time-domain (FDTD) method can model shielding enclosures with complex geometries, but has difficulty modeling wires and cables of arbitrary radii. Modeling the wire by setting the axial component of the electric field to zero in the FDTD results in a wire with a radius determined by the mesh discretisation. Neglecting wire radius in applications such as electromagnetic interference (EMI) or printed circuit board modeling may result in gross errors because near field quantities are typically sensitive to wire thickness. Taflove (1990) developed a wire modeling algorithm for FDTD analysis which models wires well for far-field calculations such as the radar cross section. The method uses a quasi-static field approximation to model wires with a user-specified radius. The wire model is reviewed and investigated for near-field accuracy via input impedance computations, since FCC class A and B regulations are tested in the near field. The input impedance for a center-fed dipole antenna is computed with FDTD methods and compared to the input impedance results from moment methods. A simulation of a shielding enclosure with an attached cable demonstrates the utility of FDTD analysis in EMC applications.