There is an exciting area of ââresearch into how the wearable devices of the future could be powered by human sweat, and at the forefront of these advancements is a team of engineers from the University of California (UC). , in San Diego. The group’s latest creation harnesses the surprisingly large sweat production at the fingertips to generate electricity when the user is sedentary or even asleep, providing a potentially 24-hour source of power.
Of the many sweat-powered sensors and wearable devices we’ve looked at over the years, the UC San Diego team have come up with a few promising examples. In 2014, scientists showed a temporary tattoo that worked like a sweat-powered bio-battery, and last year, they demonstrated a portable vitamin C sensor powered by similar means. More recently, the team developed a smart shirt that generates electricity through sweat and movement.
The recently revealed wearable device is described as the first of its kind, in that it can generate power even when the user is sleeping or sitting still. This could open up some very interesting possibilities in the portable space, as the device could potentially serve as a power source anywhere and anytime.
âUnlike other wearable sweat-powered devices, this one requires no exercise, no physical input from the wearer to be useful,â says co-lead author Lu Yin. âThis work is a step forward in making portable devices more practical, practical and accessible to the everyday person.
In developing this new type of wearable, the team had to get creative in combining a mix of components that can both absorb sweat and convert it into energy. The thin bandage-like strip is made up of carbon foam electrodes that absorb sweat and use built-in enzymes to trigger chemical reactions between lactate and oxygen molecules, which in turn generate electricity which is stored in a small capacitor.
Finger-fitting, the device takes advantage of the more than a thousand sweat glands on each fingertip that produce 100 to 1,000 times more sweat than most other parts of the body. The authors therefore describe the fingertips as 24-hour sweat factories.
âThe reason we feel more sweaty on other parts of the body is that these places are not well ventilated,â Yin explains. âOn the other hand, the fingertips are always exposed to the 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. “
Although the device generates most of its electricity this way, it is not a one-ride pony. Under its electrodes, the device also has piezoelectric material that generates additional electricity in response to pressure. This means that activities like typing, texting, or playing the piano can also lead to energy gains.
In one experiment, subjects wore the device on one finger for 10 hours of sleep, which generated nearly 400 millijoules of energy, which scientists say is enough to power an electronic watch for 24 hours. An hour of “occasional” typing and clicking with a mouse allowed the device to generate almost 30 millijoules.
âCompare that to a device that recovers energy while you exercise,â Yin explains. âWhen you run, you invest hundreds of joules of energy just to have the device generate millijoules of energy. In this case, your return on energy investment is very low. But with this device, your return is very high. When you sleep, you are not working. Even with just one touch of your finger, you’re only investing about half a millijoule.
In separate experiments, the team used their new energy collector to power chemical sensors and displays, including the aforementioned vitamin C sensor developed previously. They are now working on improving the device to make it both more efficient and durable, and hope to combine it with other energy harvesters to form new types of self-powered portable devices.
âOur goal is to make it a practical device,â Yin explains. âWe want to show that it’s not just another cool thing that can generate a small amount of power and then that’s it – we can actually use the energy to power useful electronic devices such as sensors and screens. “
The study was published in the journal Joule, while the video below provides an overview of the research.
Portable at your fingertips
Source: University of California, San Diego