Impact of microcoil shape and the efficacy of soft magnetic material cores in focal micromagnetic neurostimulation

Micromagnetic neurostimulation (μMS), despite being in its infancy, has shown promising results in spatially selective activation of neurons. The devices are micrometer-sized coils or microcoils (μcoils) which work on the principle of Faraday's Law of electromagnetic induction. Upon applying a time-varying current through these μcoils they generate a time-varying magnetic field which in turn induces an electric field that activates the neurons. These μcoils are spared from biofouling nuances as this induced electric field is not in direct electrochemical contact with the tissues. However, these μcoils have a high power of operation which lead to undesirable thermal effects on neurons. In this work, we have studied the efficacy of soft magnetic material (SMM) cores on these μcoils to solve two existing challenges for μMS. First, to minimize the power consumption for these μcoils. Second, to achieve even more precise and focal activation of the neural tissues. We have studied 3 shapes of μcoils with comparable sizes in terms of spatial contour plots of magnetic field and induced electric field. Furthermore, the efficacy of 2 shapes of SMM cores, cone and rod, of varying sizes have been studied to obtain a spatially focal magnetic field and increased magnitude of induced electric field.