New wireless charging technology harnesses fingertip sweat to top up your smartphone

Our fingertips have been far more employed than ever before since the advent of touch-screen smartphones but they are about to take on even more responsibility. Scientists from the University of California San Diego (UCSD)have developed new remote charging technology that works by harvesting sweat from fingertips and using it to generate an electric charge.

The wearable device consists of strips attached to the fingertips like sticking plasters. The strips contain enzymes that react with the chemicals in sweat to produce electricity, which is then stored and can be used to charge a small electrical device like a smartphone.

Over ten hours overnight, the device was able to generate and store 4000 millijoules of energy from a single fingertip, which is roughly enough to power an electronic wristwatch for 24 hours. One strip on each finger, however, would generate 10 times that amount of electricity, opening the door to it being used to power more energy-hungry devices like phones.

The research team behind the project admit the technology will need to be further refined if it is to be commercially viable as it would currently take 3 weeks of overnight sessions for the device to generate enough electricity to fully charge the average modern smartphone. However, it could prove useful in the shorter term as a source of energy for simple medical technology that has modes energy requirements, such as the kind of sensors that measure the glucose levels of diabetics.

The development is still a leap forward on previous research around using sweat to generate electricity, which has required users to exercise intensively to produce enough sweat to power even the least demanding electrical device.

While still in its early stages, the new technology is being hailed as a significant step towards energy-harvesting devices able to generate meaningful amounts of electricity without the need for either intense physical movement or external sources of power. Additional energy is also created by the new wearable technology if pressure is applied to the strips through activities like typing on a keyboard.

Nanoengineering professor Joseph Wang who works at UCSD and co-authored the study commented:

“We wanted to create a device adapted to daily activity that requires almost no energy investment. You can forget about the device and go to sleep or do desk work like typing, yet still continue to generate energy. You can call it ‘power from doing nothing’.”

Interestingly, the fingertips are used rather than other parts of the body, like the armpits, we might think produce more sweat. In fact, our fingertips are actually the part of our body with the highest concentration of sweat glands. Each fingertip is home to over 1000 sweat glands and produces between 100 and 1000 times more sweat than an equivalent surface area from most other parts of the human body.

Lu Yin, a PhD student at Wang’s nanoengineering lab and co-author of the research, explains:

“Generating more sweat at the fingers probably evolved to help us better grip things. Sweat rates on the finger can reach as high as a few microlitres per square centimetre per minute. This is significant compared to other locations on the body”.

“The reason we feel sweatier on other parts of the body is because those spots are not well ventilated. By contrast, the fingertips are always exposed to air, so the sweat evaporates as it comes out”.

“So rather than letting it evaporate, we use our device to collect this sweat, and it can generate a significant amount of energy.”

Hydrogel contained in the device optimises sweat absorption levels with the liquid then subsequently absorbed by electrodes made from a carbon foam containing enzymes which trigger a chemical reaction between the sweat molecules’ lactate and oxygen, generating electricity. That is then stored in a tiny capacitor to be discharged as needed.