Optimal Frequency for Wireless Power Transmission Into Dispersive Tissue

TLDR

RF wireless interfaces enable remotely powered implantable devices, but current studies operate below 10 MHz to avoid tissue absorption loss, requiring large receive antennas. The study investigates which frequencies best balance received power against tissue absorption. The authors model tissue as a dispersive dielectric, perform full‑wave and layered‑medium simulations, and evaluate load‑impedance effects to determine optimal frequencies. They find the optimal frequency remains in the GHz range, with mm‑sized transmit antennas favoring GHz and cm‑sized antennas shifting to sub‑GHz, allowing orders‑of‑magnitude miniaturization of implantable devices.

Abstract

RF wireless interface enables remotely-powered implantable devices. Current studies in wireless power transmission into biological tissue tend to operate below 10 MHz due to tissue absorption loss, which results in large receive antennas. This paper examines the range of frequencies that will optimize the tradeoff between received power and tissue absorption. It first models biological tissue as a dispersive dielectric in a homogeneous medium and performs full-wave analysis to show that the optimal frequency is above 1 GHz for small receive coil and typical transmit-receive separations. Then, it includes the air-tissue interface and models human body as a planarly layered medium. The optimal frequency is shown to remain in the GHz-range. Finally, electromagnetic simulations are performed to include the effect of load impedance and look at the matched power gain. The optimal frequency is in the GHz-range for mm-sized transmit antenna and shifts to the sub-GHz range for cm-sized transmit antenna. The multiple orders of magnitude increase in the operating frequency enables dramatic miniaturization of implantable devices.