Integral Equation Residuals for Error Estimation and Internal Resonance Detection

The performance of the four basic residual error estimators for perfectly conducting targets is evaluated in connection with the Rao–Wilton–Glisson method of moments numerical solutions of the electric field, magnetic field, and combined field integral equations (CFIEs). Results for 17 perfectly conducting test targets are used to evaluate the performance. Tangential-field residuals appear to be more reliable than normal-field residuals for assessing accuracy. Residual estimates are shown to be poor when used to assess an equation based on the same boundary condition as the residual. Residuals are sensitive to internal resonance modes associated with the complementary boundary condition and can be used to detect spurious solutions due to their presence.