Convergence of the fictitious-current model

When the fictitious-current model is applied for an electromagnetic-scattering problem, the accuracy and convergence of numerical results are sensitive to the distance δ_t between the physical surface and the mathematical surface on which fictitious current sources are placed. In this model, δ_t must be neither too small nor too large, since a small δ_t degrades the accuracy of numerical solution, and a large δ_t makes the moment matrix unsuited to numerical computation. Thus, when iterative methods are used, there is a trade-off between the convergence rate and the accuracy of numerical solution. Also, it is found that there exist resonant peaks depending on sampling distance δ_s, and the geometry of the scatterer. Therefore, when this model is used for CNR frequencies, spurious frequencies can be obtained. It is found that there is a linear relationship between δ_t and δ_s which maintains a constant condition number. Using this relation, a useful modelling method for electromagnetic problems is introduced