Design of a Closed-Loop Wireless Power Transfer System for an Implantable Drug Delivery Device

Active Implantable Medical Devices (AIMDs) have seen a significant increase in popularity in recent years due to their ability to provide continuous therapy unobtrusively. One of the key challenges in developing next generation AIMDs is the design of a safe and reliable Wireless Power Transfer (WPT) system. Standard commercial WPT components are not optimized to deliver small amounts of power or to work with other than small air gaps. We developed a near-field resonant inductive coupling WPT system with closed-loop real-time control, based on the commercial off-the-shelf components and leveraging the already integrated wireless communication system. The system was used to recharge a secondary battery and power supply the Nanochannel Delivery System (nDS). We tested the system’s robustness by varying the coil spacing to a maximum of 20mm, and by misaligning the coils laterally and angularly up to 8mm and 12°, respectively. We performed these tests by simulating battery charging from 2.8 V to 4.1 V and we tested four coils, from 6mm to 19mm in diameter, to evaluate the best trade-off between effectiveness and miniaturization. Finally, we recharged the selected battery for two distances, 2.5mm and 6.5mm. The results show that the 17mm and 19mm coils have the highest peak efficiencies of 31.3% and 32.3% (26% and 26.3% on average), respectively, and provide a complete and reliable battery recharge in less than 5 hours while keeping the receiver coil temperature within 2 °C.