Engineers at the University of California, San Diego (UC San Diego) have developed a thin, flexible strip that can be worn on a fingertip and generates small amounts of electricity when a person sweats or presses on it.
The sweat-fueled device could power a whole new generation of wearables by harnessing the energy extracted from human sweat even when a person is not moving.
“Unlike other sweat-powered wearables, this one requires no exercise, no physical input from the wearer in order to be useful,” said Lu Yin, a nanoengineering student at UC San Diego Jacobs School of Engineering. “This work is a step forward to making wearables more practical, convenient and accessible for the everyday person.”
The device also generates extra power from light finger presses such as typing, texting, playing the piano or tapping in Morse code. All of these actions can become sources of energy for future generations of wearables.
“We envision that this can be used in any daily activity involving touch, things that a person would normally do anyway while at work, at home, while watching TV or eating,” said Joseph Wang, a professor of nanoengineering at the UC San Diego Jacobs School of Engineering. “The goal is that this wearable will naturally work for you and you don’t even have to think about it.”
As fingertips are one of the sweatiest spots on the body, the bulk of the power will be produced via sweat. Researchers focused on fingertips since other parts of the body are not well ventilated whereas fingertips are always exposed to air.
How it works
The flexible strip can be wrapped around a fingertip like a Band-Air and the padding of carbon foam electrodes absorbs sweat and converts it into electrical energy.
These electrodes are equipped with enzymes that trigger a chemical reaction between lactate and oxygen molecules in sweat to generate electricity. Underneath these electrodes is a chip called a piezoelectric material, which generates additional energy when pressed.
As the wearer sweats or presses on the strip, the energy is stored in a small capacitor and is discharged to other devices when needed. In testing, 10 hours of sleep generated 400 millijoules of energy, which is enough to power an electronic wristwatch for 24 hours. Clicking a mouse or keyboard generated about 30 millijoules.
“By using the sweat on the fingertip — which flows out naturally regardless of where you are or what you’re doing — this technology provides a net gain in energy with no effort from the user,” Wang said. “This is what we call a maximum energy return on investment.”
The next steps are to make the device more efficient and durable. Future studies will work to include new types of energy harvesters to create a new generation of self-powered wearable systems.