Optimised Design and Characterisation of an Implantable Flexible Wireless Power-Transfer System Based on an LCC-S Topology

This paper proposes a flexible, misalignment-tolerant wireless power-transfer (WPT) system based on the inductor–capacitor–capacitor-series (LCC-S) compensation topology to address the low coupling efficiency and poor power stability of miniature receiver coils under complex body motion in implantable medical devices. Finite-element simulations using Ansys Maxwell are performed for flexible receiver coils with outer diameters below 20 mm to investigate electromagnetic-parameter variations at different bending curvatures. In air, the self- and mutual inductances initially decrease and then increase as the bending curvature increases. Under extreme bending (R = 20 mm), the inclined coil edges capture additional radial magnetic flux, accounting for the recovery of these parameters. In the simplified tissue model, the self-inductance increases overall by approximately 5–6% but decreases monotonically with bending, with a maximum variation of about 2.4%. System performance is evaluated through Maxwell–Simplorer field-circuit co-simulation and experimental validation. Owing to the zero-voltage-switching (ZVS) operation which the constant transmitter-coil current provided by the primary LCC network, the system delivers approximately 0.25 W of output power at a transmission efficiency above 21% at 13.56 MHz under severe bending, while the secondary side maintains a nearly constant output voltage. The resonant-frequency drift remains approximately 1.2%. The proposed design maintains stable power transfer under the tested bending conditions, without requiring complex control strategies.