Angle-Tuned Coil: A Focality-Adjustable Transcranial Magnetic Stimulator

AbstractConventional transcranial magnetic stimulation (TMS) coils are limited by the depth-focality tradeoff rule. To better utilize this depth-focality tradeoff rule, a new approach needs to be employed. In this study, a new multi-layer winding-tilted TMS coil design is proposed for human brain stimulation. It can deliver stimulation with better depth-focality characteristic than the double cone coils to deep brain regions. In our design, circular coils were accumulated along their central axis to improve the field decay rate as a function of the stimulation depth. We also tilted the winding angle of the coils to break the ring-shaped symmetry of the electric field distribution and accomplish the focality. New curves were plotted in the depth-focality tradeoff profile for our coil design, which intersected with the figure-8 coil curve. The new curves break the depth-focality tradeoff, and our coil design presents better focality than the H coils and circular coils, deeper stimulation depth than figure-8 coils, and the capability for multisite brain stimulation due to its unique structure and the limited contact area with the human head surface, which cannot be accomplished with the double cone coils.