[Design of a half solenoid coil for optimization of magnetic focusing in trans-cranial magnetic stimulation].

Trans-cranial magnetic stimulation (TMS) is the process that excitable human brain tissue is activated with the electric field induced from a changing magnetic field. Magnetic focusing characteristic is one of the most important technical considerations of coil design in TMS. In this paper, a half solenoid coil was proposed to be used in TMS and the magnitude profile of the induced electric fields in different depth was studied based on the induced electric field theory of magnetic stimulating coil. The magnitude profile of the induced electric fields produced by half solenoid coils was compared with that of butterfly-shaped coils. The result shows that half solenoid coils retain the good focusing characteristics of the main lobe of the butterfly-shaped coils. At the same time side effect of the side lobes on notargeted tissue is mitigated, which would otherwise lead to undesirable stimulation. Hence magnetic focusing is optimized, which is expected to give a more accurate delivery of the focal point for more effective stimulation.