Sweat-powered finger wrap generates energy while you sleep

15 Jul 2021

Image: © LIGHTFIELD STUDIOS/Stock.adobe.com

By using one of the sweatiest parts of the body, researchers have developed a material to power devices with no extra effort from the wearer.

Researchers have designed a flexible strip of material that is powered by your sweat and could be the solution to fueling wearable devices.

By using enzymes to trigger a chemical reaction, the thin device generates electricity from your body’s own sweat and could fuel watches, health monitors and other wearable technologies.

This type of device is the first of its kind, said co-first author Lu Yin, a nanoengineering PhD student at the University of California San Diego Jacobs School of Engineering.

“Unlike other sweat-powered wearables, this one requires no exercise, no physical input from the wearer in order to be useful. This work is a step forward to making wearables more practical, convenient and accessible for the everyday person.”

The new wearable energy harvester is described in a paper published 13 July in the journal Joule.

The research highlighted how lactate-based biofuel cells have shown promise as bioenergy harvesters to power electronics.

There is a large amount of lactate in human sweat, which means that placing these fuel cells on the human skin could mean lots of power.

The problem is finding skin that is sweaty enough.

Most locations on the skin have such a low flow rate that it isn’t possible to power anything useful.

Most places, except for the fingertips.

With more than 1,000 sweat glands on each fingertip, the rate of sweat on each digit isn’t anything to laugh at.

The fingers can actually produce between 100 and 1,000 times more sweat than most other areas on the body. The reason we don’t notice this is because of rapid evaporation due to airflow.

The technology doubles down on the usefulness of the fingertip by harnessing energy from light finger presses. Everyday activities such as typing, texting or playing the piano could all give some energy back.

“Our goal is to make this a practical device,” said Yin. “We want to show that this is not just another cool thing that can generate a small amount of energy and then that’s it – we can actually use the energy to power useful electronics such as sensors and displays.”

The researchers had a subject wear the sweat-powered device on one fingertip while doing sedentary activities. From 10 hours of sleep, the device collected enough energy to power an electronic wristwatch for almost 24 hours.

And this is just from one fingertip. Strapping devices on the rest of your digits would generate 10 times more energy, the researchers said.

“Compare this to a device that harvests energy as you exercise. When you are running, you are investing hundreds of joules of energy only for the device to generate millijoules of energy,” explained Yin.

“In that case, your energy return on investment is very low. But with this device, your return is very high. When you are sleeping, you are putting in no work. Even with a single finger press, you are only investing about half a millijoule.”

Sam Cox was a journalist at Silicon Republic covering sci-tech news