Wearable Finger Wrap Powers Small Electronics During Sleep

One of the biggest challenges in small wearable devices is getting a battery inside large enough to power them reliably without making it too bulky and heavy for comfort. Researchers at UC San Diego have developed a new wearable device that turns the touch of a finger into a source of power for small electronics and sensors. The thin and flexible strip can be worn on a fingertip and can generate small amounts of electricity when the wearer's finger sweats or presses on it.

One of the best aspects of the device is that it can generate power even when the wearer is asleep or sitting still. Researchers believe their breakthrough is potentially significant in the field of wearable devices because they can harness energy from human sweat even if the person isn't moving. Researcher Lu Yin says that, unlike other sweat-powered wearables, the one they developed requires no exercise and no physical input from the wearer.

The device can generate additional power from light finger presses with activity such as typing, texting, playing piano, or tapping becoming sources of energy. Developers believe that the device could be used in any daily activity involving touch, allowing things that users normally do to power wearable devices. Most power comes from sweat produced by the fingertips, which perspire constantly.

Fingertips are one of the sweatiest spots on the entire body, with each having over a thousand sweat glands producing between 100 and 1,000 times more sweat than other areas of the body. The reason people feel more sweat from other parts of the body is because the spots aren't well ventilated. Fingertips are always exposed air allowing the sweat to evaporate as it comes out.

The thin, flexible strip is wrapped around a fingertip like a Band-Aid with a pad of carbon foam electrodes absorbing sweat and converting it into electrical energy. The electrodes have enzymes that trigger chemical reactions between lactate and oxygen molecules in sweat to generate electricity. Under the electrodes is a chip made from a piezoelectric material generating additional electricity when pressed. From 10 hours of sleep, the device can collect almost 400 millijoules of energy, which is enough to power an electric watch for 24 hours.