A medical application of electromagnetic fields: The magnetic stimulation of nerve fibers inside a cylindrical tissue

A model is presented that predicts the electric field induced in the arm during magnetic stimulation of a peripheral nerve. The arm is represented as a homogeneous, cylindrical volume conductor. The electric field arises from two sources: the time - varying magnetic field and the accumulation of charge on the tissue - air surface. In magnetic stimulation both of these contributions are significant. A passive cable model describes the response of the nerve fiber to this induced electric field. Once the coil's position, orientation and shape are given, and the resistance, capacitance and the initial voltage of the stimulating circuit are specified, the resulting transmembrane potential of the fiber is calculated as a function of distance and time.