wireless charging of a medical implant

For medical implants it is important that batteries are powered efficiently. Sensors in the implants often require power to read out data. Therefore, batteries in the implants must be charged using a charging coil. Using COMSOL Multiphysics, the body heating due to the charging was calculated. The energy dissipation in the skin was calculated to be an order of magnitude below the maximum allowed value. The charging coil was experimentally validated by our multidisciplinary colleagues within the Demcon Group.

Controlling heat dissipation while charging

our approach.

The charging mechanism of the battery is based on two coils: a receiver (Rx) and a transmitter (Tx) coil. The Rx coil is embedded in the electrical circuit of the implant, and the Tx coil is positioned inside the external charger. COMSOL Multiphysics was used to design and optimize both coils. The objective was to ensure that enough current is generated in the Rx coil to charge the implant, while minimizing the power losses in the Rx and Tx coils and circuits. The energy that is dissipated in the surrounding skin tissue was one of the limiting design constrains.

In the COMSOL model, the Rx coil was placed 3 cm below the transmitter. The centers of the Rx and Tx coils were displaced with respect to each other by 3 cm, to mimic the real-life situation. The electrical circuit of the implant was simulated with LTspice, and experimentally verified using a breadboard.

Finally, simulations of local heating of the implant and the surrounding tissue were performed for several skin depths of the implant. For these simulations, it was needed to make a coupled EM-thermal simulation using COMSOL.


Chris Spruijtenburg

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“if anything is slightly off with one of the dozens of components, the end product will not work.”

The Kryoz is an extremely complicated piece of equipment. If anything is slightly off with one of the dozens of components, or the procedure is not properly followed, the end product will not work. That would make reverse engineering quite a challenge. To anyone who would like to try, I would say: good luck.