Optimal Design of a Wireless Charging System for an Implanted Hearing Device

Wireless power transfer (WPT) medical systems are progressively recognized as practical solutions for powering advanced micro-electronic devices, particularly in biomedical implants. These systems offer the potential to power devices such as cochlear implants without requiring invasive procedures to replace internal batteries, significantly enhancing patient comfort and device lifespan. Designing WPT systems with high power transfer efficiency presents several challenges, including the compact size of the WPT coils, the airgap distance between the external power source and the implanted device, the operating frequency, and ensuring tissue safety by minimizing power dissipation. This paper explores several strategies to optimize WPT coils and electronic converters for implantable medical devices (IMDs), focusing on designing efficient charging circuits for cochlear implants. Conventional design procedures for both square and circular coils are first considered, where each coil's geometry impacts the magnetic field distribution and, consequently, the efficiency of power transfer. Optimal design concerns are then applied, including the use of a Z-source inverter topology, which significantly improves efficiency. For the square coil, the Z-source inverter improved efficiency from 72.75% to 79.23%, while for the circular coil, efficiency improved from 74.55% to 82.31%. These improvements highlight the effectiveness of the Z-source inverter in enhancing power transfer efficiency by superior matching impedance and minimizing energy losses. The performance of these coil designs (in terms of power transfer efficiency, received power, and operating frequency) is demonstrated, providing insights into the trade-offs between coil geometry and overall WPT system performance. The findings offer valuable guidelines for the development of more effective WPT solutions in biomedical applications, with the potential to improve the functionality and longevity of implantable medical devices.