An efficient surface-impedance boundary condition for thin wires of finite conductivity

To include dispersive loss into a sub-cell thin-wire model, a new implementation of a surface-impedance boundary condition (SIBC) is proposed. The surface-impedance function is approximated in the frequency domain by a series of first-order rational functions allowing straightforward transform into time domain. The contribution of the wire radius is included in the surface-impedance function extending the model to very thin or poorly conducting metal wires. Further, the SIBC includes the direct-current (dc) resistance. The approximation for the SIBC is chosen such that the dependence on the wire radius and conductivity can be removed prior to the computation of the approximation coefficients. Consequently, the wire radius and conductivity can be varied without re-computing the coefficients. The proposed model is compared with an existing SIBC wire model based on the high-frequency approximation and Prony´s method, NEC-2 generated reference data, and analytical results. The results indicate enhanced accuracy at a reduced computational cost as compared with an existing model.