Determination of spatial distribution of induced electric fields and the gradients in inhomogeneous volume conductors exposed to time-varying magnetic fields

A mathematic model is proposed to study the effect of the inhomogeneities in the body on the behavior of nerve excitation elicited by magnetic stimulation. A finite element method is introduced for the numerical calculation. The boundary condition at the interface between two media with different conductivities constrains the behavior of induced electric fields and currents. A computer simulation shows that the site of nerve excitation is strongly affected by the interface of the two media. The proposed model is useful for the design and analysis in magnetic stimulation of the brain and peripheral nerve system as well as the study of biological effects of extremely low frequency and radio frequency electromagnetic fields.