An Improved F/C Structure for Cell-Scale Micro-Magnetic Coil

Cell-scale micro-magnetic stimulation is the process of stimulating neuronal tissues using a sub-millimeter coil. During the process, a time-varying current is fed to the micro-coil, and the micro-coil generates a dispersed magnetic field in the focal region of the tissue to create the effect of magnetic stimulation. The micro-magnetic coil has the drawbacks of small inductance, large power consumption, low-quality factor, and uneven distribution of magnetic induction. In this article, we designed an improved F/C structure, which was surrounded by a magnetic film/planar coil, and developed a method for determining the geometric parameters of the structure based on an investigation of how the pattern, thickness, spacing, and width of the magnetic shielding layer (MSL) affect the micro-coil inductance $L$ and the magnetic induction $B$ . The experimental results show: when the magnetic permeability $\mu _{r}$ of the micro-magnetic coil with the improved F/C structure is 10 ⁶ H/m, the inductance reaches 1149.3 nH, the maximum value of magnetic induction $B$ on the $Z = 800$ nm tangential surface reaches 11.33 mT, and the average value of $B$ is 5.5 mT (the $B$ value exceeds 4.28 mT in 92.6% of the area of the $100\,\,\mu \text{m}\,\,\times 100\,\,\mu \text{m}$ micro-coil); the range of action of magnetic induction is approximately $20~\mu \text{m}$ in the $Z$ -direction. It can be concluded that the micro-magnetic coil with the improved F/C structure is superior to the existing micro-coils in terms of magnetic field uniformity, action strength, and inductance value, and the increased inductance value improves the quality factor $Q$ of the coil and reduces the power consumption of the micro-magnetic coil.