Devices and sensors are getting smaller with each passing year, but some are still constrained by the need for bulky batteries or other inconvenient power sources. However, if a new proof-of-concept research projected headed by University of Massachusetts Amherst researchers pans out, the minuscule wearables of tomorrow could receive their juice via the wearer’s skin.
“We’re using the human skin, which is composed of mostly water, as a conductor,” Sunghoon Ivan Lee, a UMass Amherst researcher and assistant professor of computer science, said in a release from the school. “But human skin is one big chunk of conductive material, so there’s no distinction between the signal wire and the ground wire. So we’re using the skin as a signal wire, and air as the ground.”
Backed by a two-year grant, the team’s first take on the technology involves a battery-backed transmitter placed on the wrist and a receiver with no battery located on the finger. The power is transferred from a node on the wrist, across the skin and to the finger receiver.
“We start by putting a battery-powered transmitter on the wrist and a battery-less receiver on the finger,” he said. “As the power transfer happens, the electrode makes contact with the human skin, which emits and receives the signal. … Using something called capacitive coupling, we’re testing for the distances between the electrode and human skin, using air as a virtual ground.”
While this version of the team’s approach is locked to the wrist and finger, other applications of the technology could lead to small wearable sensors placed within an individual’s tooth or the ear, Lee said. For the next two years though, they will primarily be investigating safety limitations, whether their conduction method could support multiple sensors and whether the data itself could be transferred through the skin alongside the power.
WHY IT MATTERS
Potential healthcare implementation of this method is well-illustrated by Lee’s original inspiration for the project: bulky health sensors weighed down by their batteries.
“Our research was originally on understanding how stroke survivors use their limbs. … If we could put a sensor on the finger, we could obtain clinically relevant information on impairment level,” he said. However, “more than half [of the sensor’s space was] dedicated to batteries. … Plus, batteries aren’t flexible and can’t be put in small parts of the body.”
Meanwhile, the tooth targeted by the team could help dentists understand the pressure or moisture levels of lost teeth, while the ear sensor could carry signals relating to muscle, eye and brain activities.
THE LARGER TREND
Self- and body-powered wearables have long been a focus of ambitious R&D teams. Such devices would still be novel if released today, as self-powered projects like UMass Amherst’s, Michigan State University’s and Northeastern University-affiliated Wearifi Inc’s demonstrate.
Alternate takes on this challenge include smaller solar-powered wearables worn on the skin — an ideal approach for products like L’Oréal’s UV exposure sensor — or implanted devices that can be charged wirelessly through the skin.