Comparison of homogeneous and heterogeneous tissue models for coil optimization in neural stimulation

In stimulation of peripheral nerves by strong pulsed magnetic fields, it is desirable to produce a well‐focused activating function. Previous analyses and an experiment have indicated that quadruple coils provide many advantages. An analytical solution has been obtained for a homogeneous cylindrical volume conductor, and a finite difference numerical solution for a realistic heterogeneous model of a human forearm. In both models it has been assumed that nerves are straight and long, and therefore the activating function is an induced field derivative in the neuron direction. The magnitudes of the activating function for various coil geometries are compared for the two models.