Researchers at Carnegie Mellon University have developed a way for human skin to power battery-free devices such as medical wearables.

People with diabetes, for example, rely on continuous glucose monitors to keep track of their blood sugar, but eventually the monitor’s batteries need to charge. The same is true for a pacemaker or any mobile device, such as a fitness tracker. And batteries are bulky and require regular maintenance.

To free wearable tech from these burdens, researchers at Carnegie Mellon University’s School of Computer Science developed Power-Over-Skin, which allows electricity to travel through the human body and could one day power battery-free devices from head to toe.

“We can expect all our electronics to keep improving,” said Andy Kong, part of the team that developed Power-over-Skin. “New releases, such as smartwatches and glasses, will be able to do so much more, but it will always be difficult to get electronics onto the body because people have to think about charging them. Power-over-Skin opens the door to making these devices invisible, allowing them to do their jobs without you noticing, which is how health monitoring should work.”

Still in its early stages, Power-over-Skin (www.figlab.com/research/2024/PowerOverSkin) allows researchers to design and implement new methods of transmitting power frequencies through the human body. In the study, researchers powered small objects such as LED lights, but they envision powering smart glasses or other wearables in the future.

Kong said commercially available health-monitoring devices were often placed on the wrist, hand or chest for convenience and to accommodate easy removal. Without a battery, a small health-monitoring device could be embedded into something as unobtrusive as an earring.

Kong worked with Chris Harrison, an associate professor at the Human-Computer Interaction Institute (HCII, hcii.cmu.edu) and doctoral student Daehwa Kim to develop Power-over-Skin. Prior work demonstrated that the human body could efficiently transmit 40MHz RF without losing too much power to the air.

The CMU (www.cmu.edu) researchers used a single battery-powered transmitter that’s worn on the body to send power to receivers – objects such as a Bluetooth joystick embedded into a ring and a light-up earring. While study participants wore these devices in locations ranging from the wrist to the ankle, researchers noted a correlation between the power the devices received and their distance from the transmitter. The closer the transmitter, the more power a receiver got.

“It’s similar to how a radio uses the air as the medium between the transmitter station and your car stereo,” Kong said. “We’re just using body tissue as the transmitting medium in this case.”

Researchers needed to increase the amount of power that could be sent through the body efficiently. One method they discovered was transmitting square waves. Previous research focused on sine waves, which have a gradual curve, to transmit the power. A square wave is a pulse of power, similar to an on-and-off switch.

Kong said researchers discovered that square waves, which have right angles, resulted in more power received and were easier to generate. He said they discovered this by accident. Someone left the transmission machine programmed to square waves and to Kong’s surprise it worked better than other options when he sent power.

While there are no immediate plans to start eliminating all batteries, Kong said there’s more to learn about how they can send frequencies through the body and what kinds of devices they can power.

“I think the next step would be increasing the power by about ten times,” Kong said. “When you can power an earbud with it, that could be the first real use case to show off applications besides powering devices like fitness trackers.”