Novel Inductively Coupled Wireless Power Transfer System Based on Modified Birdcage Coils for Torso Implanted Medical Devices

Wireless power transfer (WPT) technology offers a promising solution for overcoming the power capacity limitation of implanted medical devices (IMDs). The stability in power transfer efficiency and the distance coverage of this technology both need to be improved, however. Furthermore, patient experience is frequently disregarded in current designs. Thus, this study proposes a novel inductively coupled WPT (ICWPT) system for human torso IMDs in any position and orientation. In this proposal, a "four-leg track" type coil and a modified Helmholtz coil comprise the transmitter to excite a nonzero uniform magnetic field for all components of the Cartesian axes over the torso. In addition, a single-axis coil serving as the receiver is connected to a novel I-type ferrite core. Computational results demonstrate that the power transfer efficiency improves to 1.1%-3.4% with a volume of 0.2 \times 0.2 \times 0.1 m in the torso, leading to improvements in power transfer stability and spatial coverage compared with the previous design (0.48%-3.2%). These improvements are also due to an impressive relative increment in quality factor of 37.3% for the innovative receiver, achieved without any increase in size. Moreover, the difference in charging coverage exceeds 50% when the minimum power transfer efficiency criterion surpasses 2% compared to the previous design. By complying with the limits of the IEEE C95.1 standard and the guidelines of the International Commission of Non-Ionizing Radiation Protection (ICNIRP), the maximal permissible transmitted power can reach up to 904 mW, which satisfies the power requirements of the majority of IMDs used in present clinical practice. The proposed ICWPT system could simplify some IMDs applications, particularly for upcoming multifunctional capsule robots with active motion control. Furthermore, the compact design of the transmitter would effectively improve patient comfort. To validate the computational results, an experiment was demonstrated.