Optimal Operating Frequency in Wireless Power Transmission for Implantable Devices

Abstract

Abstract-This paper examines short-range wireless powering for implantable devices and shows that existing analysis techniques are not adequate to conclude the characteristics of power transfer efficiency over a wide frequency range. It shows, theoretically and experimentally, that the optimal frequency for power transmission in biological media can be in the GHz-range while existing solutions exclusively focus on the MHz-range. This implies that the size of the receive coil can be reduced by 10 4 times which enables the realization of fully integrated implantable devices.

Energy Harvesting and Remote Powering for Implantable Biosensors

“…A recent work [65] has questioned this choice: the tissue absorption increases with the frequency only if the displacement current is omitted into the Maxwell equations (quasi-static assumption). In that case, the propagation of the electromagnetic field is governed by a diffusion equation and decays exponentially inside the tissues.…”

“…This approximation is valid with good conductors, but is not valid if the human body is modeled as a low-loss dielectric. Without using the quasi-static assumption, thus performing a full-wave analysis, the penetration depth is shown to be asymptotically independent with the frequency, until dielectric dispersion occurs at very high frequency, in the microwave range [65]. For this reason, an optimum frequency in the gigahertz range is assumed.…”

“…11. Power gain obtained by [65] using an inductive link composed of two 4 mm coils. Simulations and measurements produce an optimal transmission frequency around 2.5 GHz.…”

Optimal frequencies for inductive powering of fully implantable biosensors for chronic and elderly patients

“…This upper limit is often proposed to minimize the quantity of power absorbed by the tissues and to increase the link efficiency. Recent works based on fullwave analysis [9,10] have questioned this assumption by showing that the penetration depth of the electromagnetic fields into the human body is asymptotically independent of the frequency. Thus, ref.…”

Experimental Characterization of a 434 MHZ Wireless Energy Link for Medical Applications

“…As a consequence, the efficiency of the wireless link is strongly affected by the presence of human tissues. Accordingly, considering that loss due to the presence of human tissues increases with frequency, many near field systems that have been proposed in the literature ( [6,[9][10][11][12]20]) operate at frequencies below a few tens of MHz.…”