Energy

Kinetic energy-harvesting shoes a step towards charging mobile devices on the go

Energy-harvesting shoes could be used to power mobile devices through a charging cable, be adapted for the military or act as a power source for people in remote areas
Energy-harvesting shoes could be used to power mobile devices through a charging cable, be adapted for the military or act as a power source for people in remote areas
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Energy-harvesting shoes could be used to power mobile devices through a charging cable, be adapted for the military or act as a power source for people in remote areas
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Energy-harvesting shoes could be used to power mobile devices through a charging cable, be adapted for the military or act as a power source for people in remote areas
The researchers combined reverse electrowetting with a novel device called a bubbler
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The researchers combined reverse electrowetting with a novel device called a bubbler
J. Ashley Taylor (left) and Tom Krupenkin are claiming to have made a big breakthrough in the collective effort to turn human motion into usable energy
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J. Ashley Taylor (left) and Tom Krupenkin are claiming to have made a big breakthrough in the collective effort to turn human motion into usable energy

Through energy harvesting tiles, backpacks and insoles, there has been much talk about harnessing our kinetic energy to power mobile devices and other electronics. A team of researchers is claiming to have made a big breakthrough in the collective effort to turn human motion into usable energy, developing a new method of producing useful amounts of electricity from our footsteps.

"Human walking carries a lot of energy," says professor of mechanical engineering at the University of Wisconsin-Madison, Tom Krupenkin. "Theoretical estimates show that it can produce up to 10 watts per shoe, and that energy is just wasted as heat. A total of 20 watts from walking is not a small thing, especially compared to the power requirements of the majority of modern mobile devices."

But drawing usable energy from these theoretical calculations would pose a number of challenges for Krupenkin and his team. Devising a harvesting technique that was practical for the "relatively small displacements and large forces of footfalls," in turn making power-producing footwear a viable possibility, has been an elusive goal so far, despite the promise of devices like the PediPower shoe attachment.

"So we've been developing new methods of directly converting mechanical motion into electrical energy that are appropriate for this type of application," Krupenkin says.

Reverse electrowetting is a technique developed by Krupenkin as a new approach to high-power mechanical energy harvesting. It involves a conductive liquid that interacts with a nanofilm-coated surface to produce electrical energy. He published a paper in 2011 reporting its ability to produce high power densities from a range of mechanical forces, but there is one caveat: it requires an energy source with a reasonably high frequency, higher than that produced by human motion.

The researchers combined reverse electrowetting with a novel device called a bubbler
The researchers combined reverse electrowetting with a novel device called a bubbler

So the researchers combined reverse electrowetting with a novel device called a bubbler in an effort to bridge the gap. The bubbler contains no moving mechanical parts, but is made up of two flat plates with a conductive liquid in between. In the bottom plate, tiny holes allow pressurized gas to enter, which in turn forms bubbles. These grow in size until they make contact with the top plate and burst. The rapid, ongoing production and bursting of bubbles washes the conductive fluid back and forth to generate an electrical charge.

The researchers say that this method can produce a lot of watts relative to the surface area of the generator, with the proof-of-concept device generating around 10 watts per square meter in early experiments. They claim that theoretical estimates indicate up to 10 kW might be possible. The shoes could be used to power mobile devices through a charging cable, be adapted for the military, or act as a power source for people in remote areas and developing countries.

"The bubbler really shines at producing high power densities," says Krupenkin. "For this type of mechanical energy harvesting, the bubbler has a promise to achieve by far the highest power density ever demonstrated."

Krupenkin and J. Ashley Taylor, a senior scientist in UW–Madison's Mechanical Engineering Department, have created a startup company called InStep NanoPower, and are seeking industry partners to commercialize the technology. They have already teamed with Vibram in develop a demonstrator shoe with the energy-harvesting technology embedded in the sole.

You can hear from Krupenkin in the first video below, while the second shows him walking to power an LED flashlight. The team's research was published in the journal Scientific Reports.

Source: University of Wisconsin-Madison

POWER WALK: FOOTSTEPS COULD POWER MOBILE ELECTRONICS

InStep NanoPower footwear energy harvester flashlight walking real time

5 comments
Peter Kelly
This could be very difficult to ascertain properly, but I would question whether this is actually harvesting power that's otherwise lost, or at least efficiently! Certainly, energy is normally lost as heat, but for all of these systems it may be that the body is required to put in extra effort and that is what is used to do the charging, rather than the normal exertion. If you add extra weight then there has to be greater energy required to move it. All that would happen, in such a case, is not gathering otherwise lost energy, but merely killing two birds with one stone, so you charge as you walk slightly less effectively.
ADVENTUREMUFFINffin
Peter makes a good point. The increased weight in boots may negate the benefits, and thus just carrying more battery would be the more holistic, lowest energy system approach, at least for the hiking community.
physics314
In the end, it will be a compromise: Extra battery would work well for a few days, whereas for longer trips "bio-recharge" seems like the more likely option. It's good to have options.
Mark Salamon
I think this is a brilliant idea to harvest the strength of our own muscles for generating electricity. While it may indeed be true that shoes like these would require slightly more effort in our walking, for most of us, that extra exercise would be highly beneficial. Just consider how many people already make a point of driving to the gym on a regular basis to use a treadmill. This seems like a simple, perfect solution that contributes to health and always keeps your cell phone charged. As the article points out, it would be especially helpful in places - both rural and urban - where people depend on walking to get them where they need to go. This innovation has my enthusiastic support, and I look forward to its successful introduction in the market. I'd love to own a pair of these shoes.
AlbertLees
I think I read about this in a sci story I think it was Dune where the desert people used walking to capture moisture and to distill waste, pee, into potable water The idea is sound and later it would not be as difficult to walk
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