Imagine portable electronics that run on a free, reliable energy source. No chargers to worry about, no dropped calls because you played too much Tetris on your Droid, and an endless playlist on your iPod that’s truly endless, at least until they pry it from your (literally) cold dead hand. Well, you may not have to imagine for long.
Vladimir Leonov and Ruud Vullers of the Interuniversity Microelectronics Center have developed power supplies that can run off of your body heat. All you have to do is strap on the blingtastic headband you see here, and you’re ready to go.
OK . . . the technology is not quite ready for prime time, but it’s much more promising than lots of other proposals for systems known as “energy harvesters” that gather power that would otherwise go to waste. Consider, for example, the wasted energy in the jiggling of your own waist (assuming you have a little extra there like I do.) As you go about your day and your spare tire bounces around, all that motion represents energy that could be put to good use. It’s truly wasted waist power.
Lots of people have proposed capturing the energy in body motion through complex mechanical contraptions or piezoelectric material. Some systems consist of energy generators in the soles of your shoes. Another one would be incorporated into soldiers’ backpacks. It creates electricity as the soldier moves up and down with each step.
It’s not a new idea. There have been self-winding watches around for centuries that rely on the random motions of your arm to keep running. The problem with most of them is that the energy has to come from somewhere. It’s not a big deal if all you want to do is check the time, but as soon as you try to run something as power hungry as a cell phone, you get into trouble.
Consider the military backpack power supply. Every watt of power it produces is coming from the soldier, which means there’s less power available to do everything else a soldier needs to do. Besides wearing a grunt down faster, it will mean he or she will have to eat more to keep going. In effect, you’re replacing conventional batteries and power sources with a really inefficient generator (the soldier) that runs on k-rations.
Leonov and Vullers have a much better idea. You produce lots of waste heat, even when you’re sitting still. In fact, we have pretty sophisticated mechanisms in our bodies to make sure that extra heat escapes, and your insides stay at a very constant temperature. 
But that means your body is throwing away energy that could be put to good use. As long as there’s a difference between the temperature of your skin and the surrounding environment, then things know as thermopiles can convert the temperature difference to electricity. Using the electricity to run something like this chic electrocardiogram (ECG) shirt can actually help cool you down while keeping tabs on your vitals.
The temperature difference between your skin and the air is too small to generate much electricity, so Leonov and Vullers are working to develop ultra low power devices to go with their thermal energy harvesters. It’s a bit of a paradox though, because if you make the power requirements low enough, then why not just carry around a tiny battery? 
Well, I’ll tell you why. It’s because you get to choose between a plain old, boring, run-of-the-mill battery . . . or something like this far out blood monitoring bracelet! I’m not digging the headband energy harvester, but I would totally wear the pulse oximeter. It would go great with the ECG shirt. (Are you getting all this ThinkGeek?)
You can read more about the research by checking out the paper that recently appeared in the Journal of Renewable and Sustainable Energy.