Analytical Modeling of Small, Solenoidal, and Implantable Coils With Ferrite Tube Core

Implantable biomedical devices are required to be compact in size for reducing the harmful impact on human tissue, which poses a significant challenge for energizing the devices wirelessly. Inserting a ferrite tube into a solenoidal power receiving coil can improve the coupling between the coils for wireless power transfer yet keep the device compact. Based on the analytical effective permeability model of the ferrite tube, an analytical model of the solenoidal coil with the ferrite tube core is established in this letter. Compared to the existing models, the accuracy is significantly improved by using this new model, which is validated by both simulation and measurement in air and tissue environments.

I. Introduction

Powering implantable devices by using the wireless power transfer (WPT) technique is promising, thanks to removing the transcutaneous wires. Smaller size of the implants further reduces the harmful impact on tissue, which, however, poses a significant challenge to achieve the high power transfer efficiency (PTE) of WPT and obtain enough power for implants, under the restriction of electromagnetic exposure to the human body.