Multi-Megahertz IPT Systems for Biomedical Devices Applications

This paper investigates the main design constraints for the optimisation of an inductive power transfer (IPT) link for recharging implantable medical devices [1], and presents the potential advantages of operating in the multi-MHz range for such applications. The design proposed in this paper offers a fast charging solution, allowing patients to recharge their active medical implants every 4-5 years for 40% of its battery capability. The main challenge consists of obtaining good coupling and effective Q factor of the receiver coil, while minimizing the overall increase in size of the medical implant. Analysis obtained through electromagnetic simulations with CST Studio Suite for a 13.56 MHz, 1 W system suggests that it is possible to achieve a relatively high theoretical link efficiency of 66%, while keeping surface temperature increases and specific absorption rate (SAR) within the limits established in EN 45502 [2] and ICNIRP 1998 [3]. The experimental results show two feasible systems with different separation distances between the device's metallic case and the receiver coil, achieving transfer efficiencies [11] of 41% and 53% for separations of 1 mm and 7 mm, respectively.