Special hybrid FE/BE method for open magnetic field problems

A special hybrid method was developed combining the finite element method (FEM) with a special boundary element method (BEM) to treat open boundary axisymmetric electromagnetic field problems. The FEM, applied for the field description in an inner region bounded by a fictitious spherical surface, is appropriate to take into account complex shaped devices in the presence of heterogeneous, anisotropic or even nonlinear media. The new BEM, used to take into account the field in the open homogeneous outer region, was based on an analytical treatment in spherical coordinates, consisting on an associated Legendre function series development. The method was applied to the static magnetic field evaluation due to the current flowing trough a main coil in the air. The analytical treatment, for the external field, reduces time and memory consumption for the computer evaluation, provides effective error control, and allows the field determination everywhere. Results were compared with those obtained either from experimental or by using other numerical methods.