CSCMR WPT Systems for Wearable Devices

Traditional wireless power transfer (WPT) utilized for wearable medical devices exploits Inductive Power Transfer (IPT) utilizing Magnetic Resonant Coupling (MRC) methods. IPT can deliver very high efficiencies with the main drawback being the short distance (between 1 and 3 cm). Unfortunately, beyond the 3 cm threshold the efficiency significantly diminishes, as its attenuation rate becomes proportionate to l/r⁶, As a result, for WPT applications requiring longer-range IPT is a challenging way to go. On the other hand, MRC systems can be used for extended WPT ranges being insensitive to interference from non-resonant objects. The Strongly Coupled Magnetic Resonance (SCMR) WPT method is undeniably the most efficient, providing the longest range. Specifically, in a traditional SCMR system both the transmitter (TX) and the receiver (RX) employ two loops each. For the TX element these are a source loop and a resonator loop, and for the RX element, these are a load loop and a resonator loop. The only drawback of SCMR systems against their very high efficiency is their size posing a significant challenge for case where deployment in confined spaces is chosen. That is the reason that SCMR requires miniaturization to boost its applicability. The Conformal Strongly Coupled Magnetic Resonance (CSCMR) method which was recently introduced in (K. Bao, et al.,doi: 10.1109/ ACCESS.2019.2945319) can do exactly that. Specifically, contrary to conventional SCMR systems that require a physical separation between the source and the resonator loop for TX (or load and resonator loop for RX), in CSCMR the source/load loops are coplanar with their respective TX/RX resonator loops. Thus, the volume is significantly reduced, while high efficiency is maintained. However, even though SCMR is very efficient for power transferring, the maximum dimension of its resonators is also the maximum limit for range of operation. This challenge was addressed by a novel technique introduced in (J. Barreto et al., doi: 10.1109/OJAP.2020.2999447) effectively extending the range of operation. Specifically, a U-loop resonator which is a repeater resonator was introduced, enabling the extension of the range of WPT to distances equivalent to the size of this U-loop. Finally, continuous research on WPT for wearable applications has produced several advances in the last few years. For example, in (K. Bao, et al., doi: 10.1109/LAWP. 2019.2906069) a substantial range but also miniaturized and highly efficient (60 mm and up to 80%) wireless power system was designed for wearable applications. More recently, (Juan Barreto, Abdul-Sattar Kaddour, Hyeon Seok An, Robert F. Shepherd, Constantinos L. Zekios, and Stavros V. Georgakopoulos “Liquid Metal Nanoparticles-Infused Wearable CSCMR WPT Systems”, in IEEE NRSM 2024 Boulder, Colorado 9 – 13 January 2024) presented a novel technique where conductive threads can be doped using liquid metal nanoparticles through infusion increasing the efficiency of traditional wearable CSCMR systems over six times. In this work, we present our study when our WPT system is next to a human body as shown in Figure 1. These simulations were carried out using Sim4Life software(https://zmt.swiss/sim4life/). “This work was supported by the Air Force Office of Scientific Research under grants FA9550-19-1-0290 and FA9550-24-1-0004.”