A hybrid method for the treatment of arbitrarily oriented thin wires in edge-based finite element analysis of inhomogeneous structures

In EM penetration and EMI studies, it is desirable to estimate the power coupled into braided coaxial cables situated in a complex environment and irradiated by a plane wave. An approximate solution to the problem may be derived by employing the following two-step procedure: (i) determine the current flowing on the outer surface of the cables assuming it to be perfectly conducting; (ii) using a transfer impedance concept, find the voltage induced along the length of the inner cable surface and hence the power delivered to the loads at the cable ends by using the transmission line Green´s function. The finite element (FE) and finite difference (FD) techniques have great difficulty in modeling arbitrarily-oriented thin wires. Simple solutions such as modifying the finite element basis functions to model the 1//spl rho/ behavior of fields near the wire or altering the FDTD time-stepping equations, require that the wires be directed along the edges of an orthogonal mesh, and this, in turn, imposes severe restrictions on the cable geometry. The present authors provide a hybrid technique that combines the advantages of the method of moments (MoM) in modeling thin wires and the edge-based finite element method (FEM) in modeling complex objects. The technique is similar in concept to the hybrid CTD+MoM technique used for analyzing wires in the presence of large perfectly electrically conducting objects [Pozar and Newman, 1982]. Representative numerical results for power coupled into a braided cable situated above a perfectly conducting plate, and illuminated by a plane wave, are presented.