Self-Resonant Planar Coil on Sheet Metal for Inductive Power Transfer in Neural Stimulation Implants

This article proposes a reliable and flexible self-resonator, namely, planar coil on sheet metal (PCSM), for neural stimulation implants inductive power transfer (NSI-IPT) applications. Owing to its high-frequency deviation robustness, electromagnetic shielding, and compact design, PCSM is capable of safely receiving energy at MHz resonant frequency in neural stimulation implant (NSI). The theoretical model of the PCSM, validated by ANSYS HFSS with a mean error rate of 2.95%, comprehensively accounts for interturn and interlayer capacitance, coil layer inductance, and the effect of the human tissue environment on parasitic capacitance. Finally, the prototype with PCSM is designed, and the transfer distance and load variation experiments are conducted at 6.78-MHz frequency using fresh pork as the medium to evaluate the link’s optimal power transfer efficiency (PTE) and power delivered to the load (PDL). The results achieve good agreement with the analytical results, achieving 170.8 mW (ac–ac) of PDL with 45.2% of PTE under safety constraints.