Magnetostimulation by inductive power transfer systems

Inductive wireless power transfer (IPT) necessarily involves intense time-varying magnetic fields. As predicted by Faraday´s law, the time-varying magnetic flux due to the primary-side coupler of an IPT system induces electric field and hence current in all conductive materials which enter its field, intentionally or inadvertently. Thus, we examine the possibility of magnetostimulation or more specifically peripheral nerve stimulation (PNS) by IPT systems. Analogy is made with the gradient fields of magnetic resonance imaging (MRI) machines and it is shown that some IPT systems produce magnetic fields with intensities and time rates of change similar to those of MRI gradient fields. It is shown that at least some IPT systems should be able to induce peripheral nerve stimulation. However, because more dangerous effects such as cardiac stimulation occur at field intensities and ramp durations much greater than those required to elicit peripheral nerve stimulation, it appears that most IPT systems are still very safe even in the event that humans or animals enter the high field region in the immediate vicinity of the couplers.