Enhancing Coil Design for Micromagnetic Brain Stimulation.

This work further advances the micromagnetic stimulation (μMS) technology, which has shown the capability of stimulating the nervous system using magnetic induction in a focal region of tissue by discharging a time-varying current through a sub-millimeter size coil. However, μMS was originally based on commercial off the shelf (COTS) inductors, which are designed to maximize efficiency and minimize its losses albeit shielding off the magnetic field from reaching the neural tissue. In this work, we study and fabricate microscale coil structures for next-generation μMS devices. The coil was designed to optimize the flux injected into the tissue by using a planar square spiral coil geometry, which was previously shown to be optimal for neuronal stimulation. The results of the electromagnetic Finite Elements Method (FEM) simulations of the proposed μMS device show that even though the spiral has a fully symmetric design, it nonetheless exhibits an asymmetry in the induced electric field in the tissue that can potentially be used for activating neurons with a specific axonal orientation. Such devices could become the brain and heart stimulators of the future with their contactless ability to deliver the neuronal stimulation needed for therapeutic efficacy in patients in need of implantable cardioverter-defibrillators or pace-makers, or patients with Parkinson's disease, epilepsy.