Optimization of the devices for magnetic stimulation of the nervous system: influence of frequency-related effects and geometrical characteristics

Magnetic stimulation of the nervous system is a noninvasive technique with a large number of applications in neurological diagnosis, brain research, and, recently, therapy. New applications require engineering modifications in order to decrease power consumption and coil heating. This can be accomplished by optimized coils with minimized resistance. The aim of this study is the theoretical investigation of the influence of some frequency-related effects on the electric characteristics of non-ideal air-cored coils for magnetic stimulation apparatus. In particular, the study of the influence of the skin and proximity effect on the coil resistance and, consequently, on the dissipated energy, is addressed. Moreover, the effect of some geometrical characteristics of the coil (wire size and coil diameter) is investigated. The results show that the coil resistance increases with frequency. Moreover, the influence of the frequency is lower for squared wire sections. The dissipated energy increases with wire size whereas it decreases with coil diameter. In summary, this study could suggest that, in order to optimize the coil of a magnetic stimulator device, the use of wire with small section, squared shape and larger coil diameter could be advisable