An LCC-C Compensated Wireless Charging System for Implantable Cardiac Pacemakers: Theory, Experiment, and Safety Evaluation

The technique of wireless power transfer (WPT) via magnetic coupling resonance provides a way to transfer power wirelessly to cardiac pacemakers from external source. For wireless charging system to be used in clinical environment, this paper gives priority consideration to three technical difficulties, i.e., implantation, efficiency, and safety. The LCC-C compensation topology for pacemaker wireless charger is presented, where only one secondary side resonance capacitor needs to be implanted, and resonance compensation parameters are derived. The compensation network can make the WPT system operate at stable resonance and high efficiency. The prototype of the wireless charging system for implantable cardiac pacemaker is developed, where a thin flexible receiving unit was designed to effectively shield eddy currents in the pacemaker shell. The experiments of wireless charging through pork tissues reveal that 3.072-W power can be received from a 3.919-W power source at 300 kHz, reaching a rather high WPT efficiency of 78.4%, such that the charging is fast, i.e., the 1050 mA·h, 4.2-V Li-ion battery voltage increases from 3.98 (80% residual capacity) to 4.2 V within only 27 min, and only 3.3 °C maximum temperature rise of the pork is in safe limits. The feasibility and safety of the charging system were further evaluated by simulations of specific absorption rate and temperature rise in human tissues and electromagnetic fields in the pacemaker case.