Modeling of Resonating Closed Impedance Bodies With Surface Integral Equation Methods

Numerical solutions of various surface integral equation (IE) formulations in modeling resonating (lossless) closed impedance bodies are investigated. It is demonstrated that for certain values of purely imaginary surface impedances very strongly resonating field solutions can appear. Some of the considered formulations that are known to work well outside these resonances, e.g., for lossy surfaces, can lead to very poor accuracy or even diverging solutions at these resonances. Among the considered formulations only the combined source IEs, discretized with a mixed scheme, both avoid the nonphysical spurious internal resonances and work reasonably well at the physical (impedance) resonances.