Localization of magnetic field structure of multi-current loops on axisymmetrical model for transcranial magnetic stimulation

We calculate magnetic field distributions from multi-current loops for transcranial magnetic stimulation (TMS). In TMS, it is important to produce locally strong magnetic fields and apply eddy-currents only to the aimed cell in a deep region of the brain. First, we investigate the field structure around a single current loop. We find that a single loop generates the convexed field on a certain plane parallel to the loop surface. Second, we study an axisymmetrical model of three-current loops, i.e., a main-coil and two sub-coils, In which the fields are significantly localized in the vertical direction at a symmetrical plane on the central axis compared with that of a single loop.