University of Wisconsin–Madison professor of mechanical engineering Tom Krupenkin and senior scientist J. Ashley Taylor have come up with an innovative energy harvesting and storage technology that could reduce dependence on batteries in mobile devices. Described as an energy-harvesting technology for capturing energy from human motion, the team has created footwear with the energy harvesting components embedded within.
As you may have guessed, wearers of the special shoes could generate and store enough power to charge an array of mobile devices by walking or running. The researchers have partnered with shoemaker Vibram to create the first operating footwear energy harvester.
A shoe sole with an embedded energy harvester sits next to a first practical footwear energy harvester developed by the UW-Madison researchers’ startup company, InStep NanoPower, and Vibram.
Professor Krupenkin claims “Human walking carries a lot of energy. Theoretical estimates show that it can produce up to 10W per shoe, and that energy is just wasted as heat. A total of 20W from walking is not a small thing, especially compared to the power requirements of the majority of modern mobile devices.” He also states that using but a small amount of that energy is enough to power a wide range of mobile devices such as smartphones, tablets, laptop computers and flashlights. For example, a typical smartphone requires less than 2W.
J. Ashley Taylor (left) and Tom Krupenkin showing prototypes in their lab at the UW-Madison College of Engineering. Credit: UW-Madison College of Engineering
The researchers found that traditional approaches to energy harvesting and conversion don’t work well for the small displacements and large forces of footfalls. Taking a new route, they rely on reverse electrowetting, a phenomenon that Krupenkin and Taylor developed in 2011.
Using the reverse electrowetting approach, as a conductive liquid interacts with a nanofilm-coated surface, the mechanical energy is directly converted into electrical energy. The method generates usable power, but requires an energy source with a high frequency like a mechanical source that’s vibrating or rotating swiftly.
Walking, like most environmental motion, is a low-frequency mechanical energy source. Reverse electrowetting by itself is insufficient for generating power from these low-frequency sources. To overcome this, the researchers developed what they call the bubbler method, which combines reverse electrowetting with bubble growth and collapse.
A bubbler device contains no moving mechanical parts. It consists of two flat plates separated by a small gap filled with a conductive liquid. The bottom plate is covered with tiny holes through which pressurized gas forms bubbles. The bubbles grow until they’re large enough to touch the top plate, which causes the bubble to collapse. The speedy, repetitive growth and collapse of bubbles pushes the conductive fluid back and forth, generating an electrical charge.
Essentially, the high frequency needed for reverse electrowetting is an internal property of the bubbler approach. The researchers say their bubbler method can potentially generate high power densities, i.e., the proof-of-concept bubbler device generated around 10W per square meter in preliminary experiments, and theoretical estimates show that up to 10 kW per square meter may be possible, according to Krupenkin.
Krupenkin’s and Taylor’s harvester could directly power various mobile devices through a charging cable, or it could be integrated within a range of devices embedded in a shoe, such as a Wi-Fi hot spot between mobile devices and a wireless network. The latter requires no cables, dramatically cuts the power requirements of wireless mobile devices, and can make a cellphone battery last 10 times longer between charges.
The applications for this technology are near infinite. For example, soldiers in the field could shed the heavy batteries they carry for radios, GPS units, and night-vision goggles. It could provide a source of power to people in remote areas and developing countries that lack adequate electrical power grids.
Watch a short video about this research: https://youtu.be/RRgmFo7bZJ4
Setting one’s imagination free, how about sports applications like basketball players constantly running back and forth. If they all wore a pair of these power-pumping shoes they could power up the vendor stands at least. Or placing the technology in ice skates. Hockey games, the Ice Capades, and Disney on Ice could perhaps charge up a small nation or two. How about those mass jogging marathons, similar to one that covers five boroughs of New York and attracts thousands of participants? Those pavement pounding peds could at least light up the Empire State and Chrysler buildings at least. Dance instructors could power up their studios. Dare we say it, the sky’s not even the limit. But we digress.
Krupenkin and Taylor are seeking to partner with industry and commercialize a footwear-embedded energy harvester through their startup company, InStep NanoPower. For further information, contact them as follows: Tom Krupenkin, 608-890-1948, [email protected]; J. Ashley Taylor, 608-890-1949, [email protected]