Model for calculating the magnetic field and the current density in the vicinity of a hemitoroidal coil for transcranial magnetic stimulation

A computational technique was developed to model configuration and to predict the magnetic field and current densities in the resistive tissues of the brain. The specific configuration presented is the geometric equivalent of a coil shaped as a Slinky toy bent into a half toroid. The model consists of N single loops in series, and the planes of the individual turns are rotated by 180°/(NN-1) with respect to each other. This configuration maintains the current bundle at the point where all the turns merge, but it reduces the mutual coupling between the turns