Next-gen tech aims to recharge your wearables by passing current through your body

Are you ready for electronic devices that charge through electric current passed through your body? Well be ready as at least one study has managed to show evidence that it is possible to support ultra-low-power fitness trackers like Fitbit Flex and Xiaomi Mi-Bands thereby alleviating the need to remove them for charging purposes.

We would like our smart watches and fitness trackers to monitor the vital signs of health, but one of the main hurdles for continuous monitoring is that there is always a need to charge them. At those times, they have to be removed and so continuous monitoring isn’t possible.

Pondering this problem, Sunghoon Ivan Lee, assistant professor in the University of Massachusetts Amherst College of Information and Computer Sciences and director of the Advanced Human Health Analytics Laboratory brainstormed with UMass Amherst wearable computing engineer Jeremy Gummeson to find a solution to continuously recharge these devices on the body so they can monitor the user’s health 24/7.

In a paper published in the¬†Proceedings of the ACM on Interactive Mobile, Wearable and Ubiquitous Technologies, Lee, Gummeson and lead author Noor Mohammed, a Ph.D. student in Lee’s lab, lay out the technical groundwork and showcase the feasibility that using human skin as a conductor of electricity it is possible to support low-power devices.

Gummeson, an assistant professor of electrical and computer engineering, explains how the technology uses human tissue as a transfer medium for power. “In this device we have an electrode that couples to the human body, which you could think of as the red wire, if you’re thinking of a traditional battery with a pair of red and black wires,” he says.

The conventional black wire is established between two metal plates that are embedded on the wearable device and an instrumented everyday object, which becomes coupled (or virtually connected) via the surrounding environment when the frequency of the energy carrier signal is sufficiently high – in the hundreds of megahertz (MHz) range.

The researchers tested a prototype of their technology with 10 people in three scenarios during which the individuals’ arm or hand made contact with the power transmitter – either as they worked on a desktop keyboard or a laptop, or as they were holding the steering wheel of a car.

Their research showed that approximately 0.5 – 1 milliwatt (mW) of direct current (DC) power was transferred to the wrist-worn device using the skin as the transfer medium. This small amount of electricity conforms to safety regulations established by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and Federal Communications Commission (FCC).

“You can think of the amount of power that gets transmitted by our technology as roughly comparable to what’s transmitted through the human body when you stand on a body composition scale, hence poses minimal health risks,” Gummeson says.

There is no sensation to the person who comes into contact with the power transmitter. “This is way beyond the frequency range that the human can actually perceive,” Lee says.

The prototype currently doesn’t produce enough power to continuously operate a sophisticated device such as an Apple Watch but could support ultra-low-power fitness trackers like Fitbit Flex and Xiaomi Mi-Bands.

The UMass Amherst team aims to improve the power transfer rate in subsequent studies and says smart wearable devices also will become more power-efficient as technologies advance. “We imagine in the future as we further optimize the power that’s consumed by the wearable sensors, we could reduce and ultimately eliminate the charging time,” Gummeson says.


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