Intermittent Charging Method Making the Receiving Coil of Wireless Charging System Inside Cardiac Pacemaker

Abstract

The wireless charging system for cardiac pacemakers has not yet been clinically applied, mainly because its receiving coil is located outside the pacemaker case, resulting in poor biocompatibility and increased implantation volume. Placing the receiving coil inside the pacemaker can solve these problems. However, this approach may cause safety issues due to eddy current heating. This article solves the heating problem by proposing an intermittent charging method and optimizing the wireless power transfer (WPT) system, such as the coupling coil and the frequency. An electromagnetic model of a pacemaker WPT system is established, incorporating conductors between coupling coils with ferrite film. The analytical expression of the voltage induced across the receiving coil is then obtained. The calculation results reveal the influence of operating frequency, ferrite film thickness, and eccentricity on the induced voltage, providing guidance for the parameter design of efficient WPT systems. The simulation and experimental results of a 3.0 W WPT system indicate that under continuous energy supply, the temperature rise can cause severe burns. Using the bipolar coil and the proposed method for intermittent charging, leads to a maximum temperature rise of human tissues $1.3~^{\circ }$ C, meeting operational thresholds for adverse health effect. The values of SAR, E, and H are also below electromagnetic field (EMF) exposure limits, thus promoting the clinical applications of wireless charging system for cardiac pacemakers, and eliminating the need for multiple implantation surgeries for patients.