Wireless Charging System Considering Eddy Current in Cardiac Pacemaker Shell: Theoretical Modeling, Experiments, and Safety Simulations

Implantable cardiac pacemakers play a vital role in extending the lives of patients with cardiovascular diseases. The technique of wireless power transfer (WPT) via magnetic coupling resonance (MCR) makes it possible to wirelessly and uninterruptedly supply electricity for pacemakers from external. However, the eddy current in the metallic pacemaker shell seriously impacts the electric energy receiving by receiving coils, making the WPT system operate at low efficiency. To decrease eddy current effect and increase WPT efficiency, the precise implant position of receiving coils is theoretically and experimentally investigated in this paper. The electromagnetic model of pacemaker WPT system is built and the analytical solution of induced voltage across receiving coils is derived, which is verified by experiments. Accordingly, the minimum distance between the receiving coil and the pacemaker shell is reversely calculated for enough induced voltage. Experimental results show that supplied by a power source of 5.66 V/300 kHz, the pacemaker charging system successfully charged Lithium-ion battery from 3.98 (80% residual capacity) to 4.2 V within 30 min by a 0.15 mm thickness receiving coil implanted into 4 mm subcutaneously. On the safety of charging system, electromagnetic and thermal simulation results show that the maximum SAR and temperature rise in tissues are 36.8 W/kg and 0.66. degrees C, respectively. The results provide a theoretical and practical support for design of a wireless charging system.