Wireless Power Transmission with Uniform Power Delivery in the 3D Space of the Human Body using Resonators in Parallel

Abstract

This paper presents a novel resonance-based multicoil wireless power transmission (WPT) system for powering implantable devices inside the 3D space of the human body. This design consists of a power amplifier, a transmitter coil, a cluster of resonators in parallel configuration, and a receiver unit, working at 13.56 MHz (the FCC-approved ISM-band). The proposed cluster configuration of the resonators in parallel configuration guarantees homogenous electromagnetic fields and uniform wireless power distribution in the 3D space of the body. It localizes the transmitted power at the receiver location naturally by activating the resonators near the receiver. We have modeled the proposed inductive link and the human body with HFSS software to optimize the design and study the body's safety by evaluating the Specific Absorption Rate (SAR) level. The proposed WPT system is implemented, and the measured results show that the inductive link with multiple resonators in parallel configuration can continuously deliver power, >120 mW, wirelessly inside the 3D space of the human-torso with a power transfer efficiency (PTE) of 15%, uniformly. We have also extended the coverage area to the human forearm by paralleling resonators with the resonators in the central body. The power delivered to the load and PTE between the resonators on the forearm area are measured >90 mW and ~14%, respectively.

Multi-resonator Wireless Inductive Power Link for Wearables on the 2D Surface and Implants in 3D Space of the Human Body

“…Different multi-coil Tx array configurations, namely switching approaches, floating resonators, parallel resonators, overlapping designs, two sandwiched structures, and so on, have been proposed to increase the effective active area where that implant or wearable devices can receive sufficient power [6], [36]- [42]. In floating, switching, and overlapping states, a disconnected array may lead to multiple resonance frequency peaks [38]- [40], [41], [43], [44]. The parallel array configuration resolves this by confining energy in a closed channel, ensuring continuous propagation, delivering a consistent voltage to each array element from the PA, generating higher current at the array's coil element adjacent to the receiver, enabling automatic positioning, and optimizing power consumption [38]- [40], [41].…”

“…In floating, switching, and overlapping states, a disconnected array may lead to multiple resonance frequency peaks [38]- [40], [41], [43], [44]. The parallel array configuration resolves this by confining energy in a closed channel, ensuring continuous propagation, delivering a consistent voltage to each array element from the PA, generating higher current at the array's coil element adjacent to the receiver, enabling automatic positioning, and optimizing power consumption [38]- [40], [41].…”

“…The parallel-connected multi-resonator Tx array designs have shown excellent performance in wirelessly powering (1) wearable headstages in animal cages (for long-term in-vivo experiments with freely moving small animals), (2) IMDs, and (3) multiple smartphones simultaneously, using a single power source [40]- [43], [45]. Such configuration provides great uniformity of power transfer efficiency (PTE) and power delivered to the load (PDL), as well as enabling natural power localization property, only activating the resonator near the Rx unit with no additional circuitry [39]- [41]. However, the parallel approach with horizontally oriented Tx resonators does not efficiently deliver power to the vertically oriented implants or wearables.…”

“…The entire system (resonators) is tuned to carry the energy wirelessly at the frequency of 13.56 MHz, safe for biological tissues according to FCC-approved ISM (industrial, scientific, and medical) band and safety standards, with negligible power absorption [36]- [41]. The number of resonators, n, within a single cluster is determined by the coverage requirements of the intended application area and the separation between the Rx unit and the Tx unit.…”

“…The design of the Tx unit can be independent of the Rx unit design when the Rx unit's dimensions are much smaller than the Tx coil or Tx resonator(s) [41]. We have used the same approach to design and optimize the proposed inductive link.…”