Wearable Device Generates Electricity From Walking Knee Movements

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Wearable Device Generates Electricity From Walking Knee Movements

Posted by timothy on Sunday June 17, 2012 @09:41AM from the walk-to-work dept.

Zothecula writes "If you've ever worn a knee brace, then you may have noticed what a large change in angle your knee goes through with every step you take, and how quickly it does so. A team of scientists from the U.K.'s Cranfield University, University of Liverpool and University of Salford certainly noticed, and decided that all that movement should be put to use. The result is a wearable piezoelectric device that converts knee movement into electricity, which could in turn be used to power gadgets such as heart rate monitors, pedometers and accelerometers."

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Or.. by busyqth · 2012-06-17 09:49 · Score: 5, Funny

It could be used to power a truly awesome joy buzzer.
1. Re:Or.. by CmdrEdem · 2012-06-17 10:08 · Score: 1
  
  ...they could power my yet-to-be cybernetic implants. Why do I get the feeling that they the question they should be working on is "How can our bodies handle some metal/semiconductor inside without killing itself?"
  
  --
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2. Re:Or.. by Dunbal · 2012-06-17 10:22 · Score: 1
  
  my yet-to-be cybernetic implants
  Some of us already have cybernetic implants you insensitive clod!
  
  --
  Seven puppies were harmed during the making of this post.
3. Re:Or.. by __aaltlg1547 · 2012-06-17 10:45 · Score: 2
  
  The really cool stuff is going to have to wait for a device that extracts food (sugars or fats) and oxygen from blood and makes usable electricity so it's directly powered by food. And it would have to give priority to your body, although perhaps you could program it to help you control your weight.
4. Re:Or.. by p0p0 · 2012-06-17 10:50 · Score: 2
  
  Already done. Search slashdot for it. It'll be used to power small implants and uses sugar from the blood.
5. Re:Or.. by Jeremi · 2012-06-17 17:45 · Score: 5, Insightful
  
  Already done. Search slashdot for it. It'll be used to power small implants and uses sugar from the blood.
  That's somewhat useful, but what we Americans really need is a device that runs on the energy stored in body fat. People could connect their home gaming rig to their beer belly's AC socket, and emerge at the end of their 8-hour Skyrim session significantly slimmer than when they started.
  
  --
  
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6. Re:Or.. by Tastecicles · 2012-06-17 19:56 · Score: 1
  
  oh, to have mod points...
  
  --
  Operation Guillotine is in effect.
7. Re:Or.. by Lumpy · 2012-06-17 22:27 · Score: 1
  
  With Nuclear batteries!
  
  --
  Do not look at laser with remaining good eye.
8. Re:Or.. by amoeba1911 · 2012-06-17 22:51 · Score: 2
  
  you know some people will abuse it, plugging a hair dryer into their beer belly's AC socket and end up with hypoglycemia.
9. Re:Or.. by mcgrew · 2012-06-18 02:10 · Score: 1
  
  He's just jealous that he isn't a cyborg.
  
  --
  Free Martian Whores!
10. Re:Or.. by Anonymous Coward · 2012-06-18 03:38 · Score: 1
  
  Won't work. A device which uses the fat before it gets stored would be useful (and help people lose weight and stay thin). But if you solve the problem of getting the body to give up its fat (without side effects), you don't need the device to get thin anymore.
11. Re:Or.. by CmdrEdem · 2012-06-19 01:30 · Score: 1
  
  I`m sorry for my oversight. I hope you are not offended. I was thinking about optional hardware, that does not need autonomy as pacemakers.
  
  --
  This combination doesn`t exist: ETIs that know about humanity and want to see us dead. Otherwise we wouldn't exist.
12. Re:Or.. by uninformedLuddite · 2012-06-19 17:51 · Score: 1
  
  It will be weaponised as soon as a lobbyist can get the millions in funding released.
  
  --
  The new right fascists are bilingual. They speak English and Bullshit.
13. Re:Or.. by uninformedLuddite · 2012-06-19 17:53 · Score: 1
  
  Americans will do that in the bath. Hypoglycemia takes too long.
  
  --
  The new right fascists are bilingual. They speak English and Bullshit.
still waiting on the fart combuster. by Anonymous Coward · 2012-06-17 09:50 · Score: 1, Funny

It'll bring about a bean revolution.
1. Re:still waiting on the fart combuster. by rishistar · 2012-06-17 21:29 · Score: 1
  
  As with many business decisions it'll depend on what the accountants say. And this one may be tough to get past the bean counters.
  
  --
  Professor Karmadillo Songs of Science
More power by Anonymous Coward · 2012-06-17 10:00 · Score: 1

Finally, a way to power our future borg implants.
1. Re:More power by Anonymous Coward · 2012-06-17 10:16 · Score: 1
  
  I want to be powered by plutonium-238. There's no way I'll be able to power my arm mounted laser cannon with this thing.
2. Re:More power by Anonymous Coward · 2012-06-17 10:44 · Score: 5, Informative
  
  Finally, a way to power our future borg implants.
  Except that we already had this technology in 2008. And /. user Promatrax161 called out the idea in 2005. But then he may have adapted it from a shoe based version in 2001.
3. Re:More power by AngryDeuce · 2012-06-17 11:03 · Score: 3, Interesting
  
  I was thinking more along the lines of the stillsuit, which if I recall correctly was powered in via movement.
4. Re:More power by thesuperbigfrog · 2012-06-17 18:51 · Score: 3, Informative
  
  You are correct.
  "It's basically a micro-sandwich -- a high-efficiency filter and heat-exchange system. The skin-contact layer's porous. Perspiration passes through it, having cooled the body ... near-normal evaporation process. The next two layers . . . include heat exchange filaments and salt precipitators. Salt's reclaimed. Motions of the body, especially breathing and some osmotic action provide the pumping force. Reclaimed water circulates to catchpockets from which you draw it through this tube in the clip at your neck... Urine and feces are processed in the thigh pads. In the open desert, you wear this filter across your face, this tube in the nostrils with these plugs to ensure a tight fit. Breathe in through the mouth filter, out through the nose tube. With a Fremen suit in good working order, you won't lose more than a thimbleful of moisture a day..."
  
  --
  42
5. Re:More power by Tastecicles · 2012-06-17 19:57 · Score: 2
  
  meh. Now, where's my spare Illudium Pu-36 explosive space modulator...?
  
  --
  Operation Guillotine is in effect.
6. Re:More power by ongelovigehond · 2012-06-17 20:10 · Score: 1
  
  Sweat only cools when it evaporates, so the suit won't work.
7. Re:More power by mwvdlee · 2012-06-17 21:02 · Score: 1
  
  Sweat cools when it leaves the body, what happens afterwards doesn't matter.
  
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8. Re:More power by vrt3 · 2012-06-17 21:04 · Score: 1
  
  Citation please?
  
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9. Re:More power by ongelovigehond · 2012-06-17 21:12 · Score: 4, Informative
  
  Sweat cools because the phase transition from liquid to vapor absorbs a lot of energy to break the bonds. This energy is provided by the skin, so as a result, the skin gets cooler. Likewise, if you condense the vapor back into a liquid, the exact same amount of energy is released again. If that condensation happens inside the suit, the suit will get warm, defeating the purpose of sweating in the first place. It would be like running in the desert in a raincoat.
10. Re:More power by mcgrew · 2012-06-18 02:25 · Score: 1
  
  My eye implant is powered by the eye's muscles. Most cybernetic implants are non-electronic and likewise are powered by the cyborg's human musclature. There are probably a lot more artificial joints than there are pacemakers and cochlear implants.
  
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  Free Martian Whores!
11. Re:More power by uninformedLuddite · 2012-06-19 17:55 · Score: 1
  
  I made the mistake of seeing the movie before reading the book. It was years before I picked it up as the movie was just so awful.
  
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  The new right fascists are bilingual. They speak English and Bullshit.
12. Re:More power by uninformedLuddite · 2012-06-19 17:56 · Score: 1
  
  It's not sex
  
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  The new right fascists are bilingual. They speak English and Bullshit.
Bending, not lateral movement by QuasiSteve · 2012-06-17 10:32 · Score: 2

You could actually read the article.. only takes a few seconds.

Known as the pizzicato knee-joint energy harvester, the device fits onto the outside of the knee. It is circular, and consists of a central hub equipped with four protruding arms, surrounded by an outer ring bearing 72 plectra (a plectrum is a plucking tool, such as a guitar pick). The ring rotates about a quarter of a turn with every bend of the knee, causing the plectra to pluck the arms. This causes the arms to vibrate (not unlike a guitar string), and itâ(TM)s those vibrations that are used to generate electrical energy.
a sucker born every day. by starworks5 · 2012-06-17 10:38 · Score: 1

Great instead of using a small battery, so now i can walk around with 2 knee braces, while conveniently trickle charging my ipod.
1. Re:a sucker born every day. by dogbert_2001 · 2012-06-18 01:58 · Score: 1
  
  Great instead of using a small battery, so now i can walk around with 2 knee braces, while conveniently trickle charging my ipod.
  Soon, they'll create a device that uses urine, so you can tinkle charge your iPod.
Travel! by rbowen · 2012-06-17 10:40 · Score: 5, Funny

You could even use the power generated by your knees to travel from one place to another!

--
Apache guy, Open Source enthusiast, runner
1. Re:Travel! by Trepidity · 2012-06-17 10:42 · Score: 1, Insightful
  
  At 2 mW currently, with hopes of raising that to 30 mW, you won't be traveling very fast...
  
  --
  10 PRINT CHR$(205.5+RND(1)); : GOTO 10
2. Re:Travel! by rbowen · 2012-06-17 10:45 · Score: 4, Funny
  
  I was talking about "walking." It was funny. Now it's not any more. Thanks a lot.
  
  --
  Apache guy, Open Source enthusiast, runner
3. Re:Travel! by lobiusmoop · 2012-06-17 10:57 · Score: 3, Interesting
  
  Quick comparison with a regular AA battery... they are usually around 2000mAh, 1.5V, or about 3Wh energy. So about 1500 hours of constant knee movement at 2mW. Assuming a generous 4 hours/day of walking, this generates the equivalent of a single AA cell every year. Meh.
  
  --
  "I bless every day that I continue to live, for every day is pure profit."
4. Re:Travel! by GoodNewsJimDotCom · 2012-06-17 11:41 · Score: 1
  
  Walking isn't funny, unless someone is wearing a knee brace thinking they're harvesting free energy.
  
  Silly walks are also funny. And it is well known that funny things can help us heal, relieve stress and have a longer lifespan.
  
  If I was a leader of a country, I'd have a ministry of silly walks in order to improve health care.
  
  --
  God spoke to me
5. Re:Travel! by Anonymous Coward · 2012-06-17 12:21 · Score: 2
  
  It's not quite as bad as your math. For one things, AA batteries do not stay at 1.5v, they slowly drop eventually reaching close to 1v when they are dead. A better estimate would be 1.2/1.3v. Also, this is the initial stage, they want to eventually improve it to "provide at least 30 milliwatts" which is quite better then the 2mW figure you are using as it's not like this will be out on the market right away.
  But yes, I really don't see the point. Those small lithium cell batteries would provide years of life for this scale of power while being simpler and less annoying then a wearable device that may eventually break. This device provides no extra benefits, is more complex, and in the end, feels pretty gimmicky. I also have trouble seeing it being cheaper though admittedly, those small lithium batteries can be pricey sometimes.
6. Re:Travel! by reboot246 · 2012-06-17 16:20 · Score: 1
  
  Yeah, you'd be better off with solar cells on your cap, or maybe a wind-powered generator on your head?
7. Re:Travel! by mwvdlee · 2012-06-17 21:06 · Score: 1
  
  It wasn't all that funny before. But you having to explain it makes it funny.
  
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8. Re:Travel! by Anonymous Coward · 2012-06-17 22:48 · Score: 1
  
  Head-mounted wind-powered generator for teh win(d)! I totally dig that!
9. Re:Travel! by cyberchondriac · 2012-06-18 06:30 · Score: 1
  
  Here ya go ...
  http://www.kleargear.com/1334.html
  
  --
  
  Look back up at my post, now look back down, you're on the Internet. Now look back up. I'm a signature.
10. Re:Travel! by Agent0013 · 2012-06-18 06:49 · Score: 1
  
  How about a solar-powered pith helmet with a fan. Link
  
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Re:What about your feet? by __aaltlg1547 · 2012-06-17 10:41 · Score: 1

The hip would be much better. It moves through a larger arc while walking and is powered by stronger muscles. But I suspect the energy-harvesting device would be even less comfortable than the knee brace.
Failure by hort_wort · 2012-06-17 10:53 · Score: 4, Insightful

I'm willing to go out on a knee here (sorry) and declare this experiment a failure. They have generated 2 milliwatts. Milliwatts -- my spellchecker doesn't even recognize that. For $15, I could get a 1,000 milliwatt solarpanel, tape it to my dang knee, and just sit there. Peizoelectric tech has amazing applications, but this one appears to be a dud.
1. Re:Failure by Yosho-sama · 2012-06-17 12:12 · Score: 2
  
  "So far, the device has been able to harvest about two milliwatts of power. The researchers, however, believe that it should be a relatively easy to improve its performance to the point that it is able to provide at least 30 milliwatts – this ought to be enough to power a GPS tracking system, and to allow for advanced signal processing electronics, plus more frequent and longer wireless transmissions."
  
  Put that into perspective for whoever is giving this guy mod points. This device is in prototype stage. It has functional applications at a level which the inventors think would be an easily accomplished goal. Solar or batteries can be unavailable/cumbersome. I think the idea of this project is functionality at any time necessary.
  
  --
  My kingdom for a donkey!
2. Re:Failure by bemymonkey · 2012-06-17 17:09 · Score: 1
  
  Not only that, but their "We could some day generate up to XX milliwats!" figure is 30! 30 mW is the dream number! I can generate more than that scooting my ass on the carpet, and the battery weight required to provide 2-30mW over a period of days is pretty much neglible (a 10 Wh lithium ion battery doesn't weigh a lot and will last 5000 hours (@2mW) or 333.33 hours (30mW). And as a reminder, most smartphone batteries are around 7Wh now and they're tiny and weigh practically nothing, so using that 30mA dream firgure, we could save maybe 30-40g of battery weight by strapping a power generating contraption to our knees... and that probably weighs more than the battery weight saved.
3. Re:Failure by Tastecicles · 2012-06-17 20:09 · Score: 1
  
  this got me wondering if this is a poor attempt at distraction, since modern dry batteries use lithium. There is an obscene amount of lithium in Afghanistan. Enough to ensure the financial stability of a medium sized country. Or offset the military expenditure of a large one.
  
  --
  Operation Guillotine is in effect.
4. Re:Failure by ongelovigehond · 2012-06-17 20:50 · Score: 1
  
  The energy doesn't come out of the tree. It comes out of the electrodes. The tree is only there to provide the electrolytes. It's much easier to put those electrolytes in a small container, and put the electrodes in there. That way you can carry it around, instead of having it rooted in the ground.
5. Re:Failure by Anonymous Coward · 2012-06-17 21:24 · Score: 1
  
  Keep in mind a parallel of Moore's law -- Koomey's law, which states that the amount of energy taken to perform calculations decreases over time. There are already completely integrated sensors with RF transmit capability that can operate on as little as nanowatts. Of course, this is all a matter of duty cycle but milliwatts of continuous power is plenty of power for a lot of sensing applications.
  Here's an example: http://www.eecs.umich.edu/eecs/about/articles/2011/millimeterscalecomputing.html
6. Re:Failure by necro81 · 2012-06-18 02:27 · Score: 1
  
  Indeed. You could probably harvest as much energy from the temperature difference between the skin and air, or from the quivering of the leg muscles themselves, or even from the static charge you pick up while walking on carpet!
7. Re:Failure by necro81 · 2012-06-18 02:28 · Score: 1
  
  Correction: power, not energy.
Re:Next up ... by PNutts · 2012-06-17 11:13 · Score: 5, Funny

Sex Power!
Well, since this is /. you're talking about something that mounts to one wrist.
I used to charge my phone in the wall socket once, by Anonymous Coward · 2012-06-17 11:53 · Score: 1

just like you. But then i got a wearable piezoelectic device to the knee...
The human dynamo by namgge · 2012-06-17 12:29 · Score: 4, Interesting

Walking is a very low-energy form of movement that relies on some highly evolved bio-mechnics. Attempting to harvest a useful amount of energy introduces dissipation in parts of the 'mechanism' that have not evolved to handle it. The result can be anything from mild discomfort to quite serious injuries. So, such techniques are limited to a few mW, and are in most respects inferior to using a battery.
It's been years since I saw a bicycle with a dynamo on it for similar reasons.
1. Re:The human dynamo by MarcoAtWork · 2012-06-17 12:35 · Score: 1
  
  that is because people running dynamos (usually randonneurs and/or long-distance cyclists in general) run hub dynamos, which are more efficient and don't chew your tires... as much as I agree that likely anything impinging on the walking mechanics could cause injuries, it really depends by the kind of dynamic resistance this type of device has and in which part of the walking cycle it would provide it.
  
  --
  -- the cake is a lie
2. Re:The human dynamo by ongelovigehond · 2012-06-17 20:20 · Score: 1
  
  My bike has a dynamo, mounted in the hub. The extra force required to power it is quite small compared to the power already required to propel the bike, and it doesn't change anything the biomechanics of pushing the pedals around.
3. Re:The human dynamo by namgge · 2012-06-17 21:23 · Score: 1
  
  I was referring to this type of dynamo:
  http://en.wikipedia.org/wiki/Bottle_dynamo
  which generates about 5W with an efficiency of about 50% and damages tires in the process.
  I couldn't think of a car analogy.
4. Re:The human dynamo by olau · 2012-06-17 23:01 · Score: 2
  
  Reelights and Free Lights are examples of non-friction (in the mechanical sense) dynamos that are becoming quite popular. They don't generate an awful lot of power, but enough for LED safety lights, which is all you need if you live in a city with street lamps.
5. Re:The human dynamo by dunkelfalke · 2012-06-18 00:27 · Score: 1
  
  You don't see a bicycle with a dynamo for two reasons
  1) A large part of bikes sold are MTB-wannabes, they don't have a dynamo in first place since they are meant for sports.
  2) Most bikes sold with a dynamo come with a hub dynamo nowadays. The better ones have got an efficiency of 60%-70%, depending on the speed (higher speed means lower efficiency due to eddy current, higher bearing friction and so on). Still, you get a guaranteed 3W at 6V. You can even charge your phone with it, in addition to the lights. Still, a loss of 2-3W while biking is mostly negligible. You get way more loss if you use knobby tyres on a paved road.
  
  --
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6. Re:The human dynamo by cellocgw · 2012-06-18 04:42 · Score: 1
  
  Just what I was going to write. The basic rule is TINSSTAFL.
  The only time you get energy "for free" is when the energy would otherwise have been dissipated as heat. Oblig car example: heating cabin air w/ engine heat that would otherwise have dumped into the radiator.
  I had a bicycle dynamo as a kid. I got a bright light and an exruciatingly tiring ride. It was like riding up a steep hill all the way. Hanging stuff off a knee brace will be no different.
  
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Good luck... by fahrbot-bot · 2012-06-17 12:47 · Score: 3, Funny

...wearing that through a TSA checkpoint and onto a plane.

--
It must have been something you assimilated. . . .
Perspective by subreality · 2012-06-17 12:59 · Score: 2, Interesting

At 2 mW, you'd have to walk for over 1000 hours to generate the energy held in 1 AA battery. Rather than strapping a wonky device to my knee, I'd rather just carry a spare battery.
Related, my bug out bag doesn't contain a hand-crank radio or flashlight. It has a couple packs of AAs, which are much lighter than the food to replace the energy I'd expend cranking. They'll last me at least a few weeks. If civilization can't reestablish itself in that time, I'm probably fucked, regardless of electricity.
1. Re:Perspective by bemymonkey · 2012-06-17 17:12 · Score: 1
  
  "Related, my bug out bag doesn't contain a hand-crank radio or flashlight. It has a couple packs of AAs, which are much lighter than the food to replace the energy I'd expend cranking. They'll last me at least a few weeks. If civilization can't reestablish itself in that time, I'm probably fucked, regardless of electricity."
  Have you considered a foldable/rollable solar panel? I've seen 10W (with bright sunlight) panels from $150, which is pretty awesome IMO :)
  I want one for my Thinkpad :D
2. Re:Perspective by subreality · 2012-06-17 17:53 · Score: 1
  
  I have a 5W panel so I can run the radios at home, but I'd never bother carrying it. It's a lot bigger and heavier than the batteries, and spare batteries are relatively trouble free. :)
3. Re:Perspective by bemymonkey · 2012-06-17 18:19 · Score: 1
  
  How heavy is it exactly?
4. Re:Perspective by subreality · 2012-06-17 18:40 · Score: 1
  
  Perhaps a pound. It's a 1 square foot glass panel, not a roll-up. http://amzn.com/B0006JO0TC Not that heavy, but neither are batteries.
5. Re:Perspective by bemymonkey · 2012-06-17 18:51 · Score: 2
  
  Ah ok, I wouldn't like to carry that around either... I'm considering a fold-up 10W panel right now, which should weigh in at a similar weight, but I'm assuming I'll get 5W out of it at best... I suppose you use yours solely for charging a battery, which then powers the radios?
  I'm hoping to somehow transform up to 19V and then charge my Thinkpads (which idle just under 5W) with the 10W panel... might actually be enough to charge on particularly bright days, and enough to maintain charge level on not so sunny days.
6. Re:Perspective by subreality · 2012-06-17 19:48 · Score: 2
  
  Yes, I just charge a small 12v gel cell and then use DC-DC converters to get whatever voltage I need.
  I'm not sure if the Thinkpads will charge from a 10W panel. The power port doesn't connect directly to the battery. There's a charging circuit which regulates current to the lesser of what the battery or power supply can handle. So if you connect a 65W power supply, the charging circuit pulls until it sees the voltage start dropping (which happens sooner than a 90W power supply), then just holds that charge rate. The trouble is the charging circuit may decide something is wrong when the voltage starts dropping when it's only pulling 10W.
  Fortunately, it's easy to try out! What you need is a "dc-dc boost converter", aka a "step up converter". Like this: boost converter. Warning, Chinese seller; it'll take a couple weeks to arrive, but I've bought buck converters (convert DC down instead of up) from them a couple times and never had a problem. Take one of those and try converting up from a 12V wall wart and see if it works before you get the panels.
  One potential problem: the voltage out of the solar panels will vary with load. Mine goes up to about 20V with no load. The boost converter will not convert down. There are two ways to address it: either add a small gel cell battery to hold the voltage near 12V, or use a buck-boost converter. That's just what it sounds like: boost the voltage up to say 35V, then convert back down to 19V. Of course you take a double hit on conversion efficiency doing this. It's likely not a real problem though; the laptop probably won't care, and as soon as it starts pulling power it'll go right back into the range the boost converter can handle.
7. Re:Perspective by bemymonkey · 2012-06-17 20:07 · Score: 1
  
  Those are some very interesting points, thanks. I was actually thinking more along the lines of the Thinkpad car charger, which takes a 12V input that should be more in line with most solar panels. I'm also hoping it'll be more tolerant of voltage drops and overvoltage :)
  That buck boost converter looks interesting though - I'll keep it in mind :)
8. Re:Perspective by subreality · 2012-06-18 19:50 · Score: 1
  
  Car chargers are usually just boost converters. With the higher rating it'll push more current when connected to a battery, but it will probably perform about the same given a 10W source.
I used to generate electricity like you ... by dbIII · 2012-06-17 13:52 · Score: 4, Funny

I used to generate electricity like you, but then I took an arrow to the knee.
A similar method to harness body heat? by Ka+D'Argo · 2012-06-17 15:58 · Score: 1

I've done some real basic searching online never turned up much (I didn't dig too deep) but is there a method to say hook some kind of heat absorbing sensors to the human body, store that heat and charge a battery up? I ask cause, time to time when I get hot and sweaty which is fairly easy for an overweight dude, the cheeks on my face stays incredibly warm for a long time. I also can get the "alcohol flush" from the tiniest amounts of alcohol as well where the face stays very warm and kind of reddish since the blood is closer to the surface. I'm not saying I could power anything of huge significance but I'm curious whenever I get these hot streaks for whatever reason just what body thermal energy I could get from my face in terms of battery supply.

--
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1. Re:A similar method to harness body heat? by Tastecicles · 2012-06-17 20:14 · Score: 1
  
  a thermocouple would work, I don't know how many you'd need to say, power an mp3 player though...
  
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  Operation Guillotine is in effect.
2. Re:A similar method to harness body heat? by ongelovigehond · 2012-06-17 20:25 · Score: 1
  
  It would theoretically be possible, but it would make you even less comfortable. Also, it's only possible to extract energy out of a temperature difference, so it would only work when your skin is hot, and the surrounding air is cool. In hot weather, the device would be ineffective.
3. Re:A similar method to harness body heat? by Anonymous Coward · 2012-06-17 20:55 · Score: 2, Informative
  
  There's wristwatches that do that -- look up seiko thermic.