University of California San Diego engineers have developed a wearable device that harvests energy from sweat produced by a fingertip. The flexible device wraps around the finger like a band aid. It can harvest energy when the wearer is at rest or in motion. Finger pressure also provides power to the device.
By orienting the device to the fingertip, the engineering team took advantage of a little-known fact; fingertips perspire constantly. Unlike well-known sources of sweat such as armpits, the surface of the fingers is almost always exposed to good ventilation, so perspiration evaporates rapidly.
The new device requires only a small amount of sweat to remain energized. This means that fingertip sweat can even power it during sleep. In designing the device, the team used innovative solutions to increase sweat absorption and enhance the process of converting chemical reactions in the sweat to energy. They lined the device with carbon foam electrodes that absorb a maximum amount of sweat from the small surface area covered by the wearable. The carbon electrodes contain enzymes that cause a reaction between oxygen and the lactate molecules in perspiration. That reaction releases the electricity that powers the device.
A piezoelectric chip nestled between the carbon foam and the flexible outer layer also generates electricity when the user puts pressure on the device. Typing, texting, clicking a mouse, playing piano, or simply drumming the fingers on a desk provide extra power to the new wearable. Wearing devices on all fingers would increase power output tenfold.
The wearable stores energy harvested from sweat or pressure in a tiny capacitor. In tests, the team monitored energy collection and storage collected while a wearer slept for 10 hours. Those tests demonstrated that discharging that stored energy would power an electronic wristwatch for 24 hours. Another trial showed that wearing the new device for 2 minutes, or pressing the device ten times every ten seconds, successfully powered both the energy-harvesting device and a low-power digital display.
Published in the journal Joule, the research findings suggest the device has significant potential as a sustainable power source for wearable technology. Continuous power for remote monitoring wearables could improve the integrity of data collection and provide additional security about using wearables to monitor patients with life-threatening health conditions. The engineers plan further research to improve the device’s durability and efficiency and explore combining it with other energy harvesting options.