Double Butterfly Coil for Transcranial Magnetic Stimulation Aiming at Improving Focality

It is important to improve the focality of the transcranial magnetic stimulation coil in order to minimize the undesired effects when the induced electric field exceeds the excitation threshold of the nontarget tissues. In this paper, a new double-butterfly coil was proposed and a simulation model as well as an experimental setup was developed to validate the performance of the new stimulation coil. Focality of the double-butterfly coil was compared with that of the butterfly coil via both simulation and experiment method. It is showed that the focality of the proposed coil has better focality than the butterfly coil. The effects of structural parameters on the focality performance of the induced electrical field were carefully studied.