Decomposition Of The Moment Method Impedance Matrix Into Quasi-Static And Residual Components

Since 1968 when Harrington first introduced the use of the moment method in electromagnetics [1,2], the coefficient of the unknown currents has been characterized as an "impedance" matrix. Since then a large body of work has appeared in the literature extending and refining this technique. Recent efforts to discover faster ways of filling the impedance matrix in MININEC [3,6] have resulted in a new interpretation of the impedance matrix. By extending the concept of separating the Green's function into singular and nonsingular parts to an additive decomposition of the impedance matrix, three matrices are defined: a static elastance matrix which alone determines the static charge; a static inductance matrix which, combined with the elastance matrix determines reactive behavior below resonance; and a residual frequency dependent matrix. Using the quasi-static solution and a first-order approximation for the residual mat.rix, an equivalent circuit valid up to about one-half of the resonant frequency was obtained.