Magnetic stimulation of the nervous system: Induced electric field in unbounded, semi-infinite, spherical, and cylindrical media

Knowledge of the electric field that is induced in the brain or the limbs is of importance in magnetic stimulation of the nervous system. Here, an analytical model based on the reciprocity theorem is used to compare the induced electric field in unbounded, semi-infinite, spherical, and cylinder-like volume conductors. Typical stimulation coil arrangements are considered, including the double coil and various orientations of the single coil. The results can be used to determine when the influence of the boundaries is negligible enough to allow the use of more simplified geometries.