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Knee Brace Stores Residual Energy

ANDREA SEABROOK, host:

While you're walking around, up on your treadmill or strolling through the neighborhood, think of all the energy you're wasting. This past week a team of researchers announced that they've captured the excess energy generated by walking by strapping on a specialized three-and-a-half pound knee brace, then storing that energy in a battery. The battery can power all those electronic gadgets that seem to be taking over our lives.

Professor ART KUO (University of Michigan): You can walk for one minute to get ten minutes of talk time for a current (unintelligible) cell phone.

SEABROOK: That's Art Kuo. He's an associate professor of mechanical engineering at the University of Michigan and he's one of the inventors. I asked him what this contraption looks like.

Prof. KUO: It doesn't look too different from an athletic knee brace or something that you would wear after a knee injury. But what's different about it is that it has a small device added onto it that takes motion of the knee and it transforms that into electrical power.

SEABROOK: What is going with walking that generates the energy?

Prof. KUO: Well, there's all this motion going on and it would be easy to use as you drive a generator. But I think what's different about our device is that were looking for a point in walking where there's energy that's just being wasted. We found the best place so far to steal energy from the person is near the end of what we call the swing phase of walking, when one leg is off the ground and your knee is extending. There's a point where you're actually breaking the knee, you're slowing it down right before your foot hits the ground.

SEABROOK: Okay. Hold on. I see. I think I see that. I'm trying to do it here. Okay, so you've picked your foot off the ground, picked up your foot, you've moved it forward to make a step but it's sort of in that moment before it's fully extended to take a step.

Prof. KUO: Yes. And you may feel your hamstring pulling. That's the muscle that slows down your knee.

SEABROOK: Wow. So does it work to put the brace on and, like, go shopping in the mall or stroll around? Or do you have to be constantly moving, sort of with purpose walking?

Prof. KUO: It definitely works best when you're walking purposefully. But I would say that our current problem is that all we've done is produced a prototype, which is a proof of concept. And there's still a lot of development to be done to reduce the weight and the size, make it comfortable to wear, and then it's something that someone might not mind wearing while they're walking around.

SEABROOK: What do you think this will be good for? I mean, these days we're all talking about having little solar panels to charge our cell phones and iPods. What do you envision this being used for?

Prof. KUO: In the Western world it's true. Even though it is a hassle to deal with the battery in your cell phone, you don't mind carrying it around and you are able to charge it. But a quarter of the world's population actually does not have ready access to electricity. And for them battery power is part of their livelihood. And the military also, your typical soldier carries many pounds of batteries and their livelihood depends on batteries for navigation and communication.

And we could imagine people like them using a device like this to reduce their battery load.

SEABROOK: You've called this a cocktail napkin idea. Did you actually have it at a party and did you actually write it down on a cocktail napkin?

Prof. KUO: My recollection was that we were at a conference somewhere. This is Max Donnelin(ph) and I. He's the principle investigator. And we were discussing something peripherally related and it came to us in a flash. And in fact we didn't even need the cocktail napkin. We were quite convinced that the principle made sense, but then there was still the problem of how to demonstrate that.

This was an idea that came about very quickly and easily and then was followed by several years of hard work.

SEABROOK: Art Kuo is a professor of a mechanical engineering at the University of Michigan. Thanks very much, professor.

Prof. KUO: Thank you. That was fun. Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

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