A lightweight, flexible thermoelectric fabric called Power Felt could generate enough electricity from body heat to power a small electronic device, like an iPod, or iPhone.
The fabric, composed of carbon nanotube/polymer thin films, was developed by a team headed by researchers at Wake Forest University's Center for Nanotechnology and Molecular Materials. Power Felt generates an electrical charge from temperature differences, converting thermal to electrical energy. Examples include the difference between room temperature and body temperature, or between the temperature of a jacket liner next to the body and that of a jacket exterior exposed to cold air. Alternately, the fabric could be layered under roof shingles, line car seats, be wrapped around hot water pipes, or be integrated into a wound wrap to power medical monitors.
Alternating p-type (red) and n-type (green) nanotube/polymer heterogeneous thin films, with insulating polymer films (blue) between the conduction layers, form a lightweight, flexible fabric that could generate enough electricity from body heat to power portable electronic devices. (Source: Wake Forest University)
The fabric consists of a carbon nanotube/polymer composite thin film comprising multiple layers of multiwalled carbon nanotubes and polyvinylidene fluoride. The multiple layers are alternating p-type and n-type nanotube/polymer heterogeneous thin films with insulating polymer film layers between conduction layers. Layers are pressed together vertically and heated to about 425K to 450K to melt the polymer enough to bond the layers together and form a felt-like fabric. The resulting thermoelectric voltage results in increased power output as layers are added.
Generating electricity with thermoelectric material requires high efficiency levels. High-efficiency materials, usually made from bismuth telluride, have been used for CPU cooling and mobile refrigerators, but their cost (as much as $1,000 per kilogram) makes them too expensive for high-volume consumer applications. The researchers say Power Felt can be less expensive to manufacture, lighter, and easier to process than bismuth telluride, so it is more suitable for a number of applications, including portable electronics.
Kirk, I don't understand your critique. The iPhone is the most well-known cell phone, and our headlines have to be short. Ergo the headline we chose. Generally, lead sentences and paragraphs also need to be short and concise (which are not always the same thing), ergo the lead sentence we chose.
Reading the title of this article and the first paragraph has left me at a loss for words.
Is the author commissioned by Apple to write the article? Or is it just that all journalism students are weaned on the idea that Apple provides the only technology on planet earth? There appears to be no valid reason to relate this technology to a specific manufacturer.
Perhaps a more appropriate title should have been "Wearable Fabric Could Power Your Mobile Devices"
and the first paragraph should read:
"A lightweight, flexible thermoelectric fabric called Power Felt could generate enough electricity from body heat to power a small electronic device, like an MP3 Player, or Mobile Phone."
Having played some with generating power from bismuth telluride modules, I have to wonder what they think "high efficiency" is. To me it's dismal, and the fabric will fare no better. You need high delta-T, established by high heat flux, to get any useful output. A well-heat-sinked 20W Peltier module on my stove was hard pressed to power its own cold-side muffin fan, whose draw is something like an active iPhone (tens of mA). At a much higher delta-T than a human body would produce against any tolerable ambient. You can't have high heat flux at the skin, and comfort both. Defeats the whole purpose and function of clothing.
The energy harvesting space is the new home for snake oil. Yeah, the energy you collect (over a period of hours) can power your portable device (for a period of seconds to minutes). Those bits of info never seem to escape the editing process when marketing runs the show.
I don't have all the details, but there are quite a lot in the journal article I linked to in my article:
http://pubs.acs.org/doi/abs/10.1021/nl203806q
Unfortunately, it's a for-pay article, although the university's PR office sent me the original, which of course I can't share. In any case, thermoelectric fabrics and materials are different from some of the other schemes I've seen, they appear to be more efficient, and this one seems to be a much more efficient energy-harvesting method. Plus, because it's wearable, it's supposed to be continuous.
I re-read this article, Ann, and now I am wondering how long this material could power an iPhone. That seems like it would take a pretty fair amount of current compared to the tiny sums I've seen in energy harvesting.
@Chas - I was wondering the same thing. What happens when you are not wearing anything to be powered. On top of that, with some concerns about the unknown effects of power lines and such, I wonder what the acceptance will be about having your body wrapped in a generator. Not saying I agree with those concerns, but if the questions are out there....
Good question, TJ. Since the lead author on the journal article, Corey Hewitt, mentions several different uses that are exercise and sports related, he may have already thought of that. I suspect this would be much less of a problem if it's used in a jacket liner material.
The material works in the lab. I'm interested in use in the real world. Put the jacket on, head outside.
How will PowerFelt perform when the wearer perspires? When it rains?
Earphone wearers who exercise frequently complain when their stereo headsets stop working because of perspiration. One would expect similar problems with anything electrical in nature in close proximity to the human body.
Walt is correct. Energy is generated from a temperature differential, for example, as the story says, "between the temperature of a jacket liner next to the body and that of a jacket exterior exposed to cold air." In that case, the generation of electricity would not cool down the wearer of the jacket. This is explained in more detail in the journal article. I don't recall seeing anything about static electricity, and I don't see why that would occur with this material. If it did, I suspect the material would likely make use of it.
Kevin, thanks for your comments. As the story points out, current high-efficiency TE fabrics like bismuth telluride are very expensive, and this particular fabric is aimed at high-volume low-power consumer apps, or medical apps like wound wraps, which those more expensive materials don't or can't address. What other types of applications did you have in mind?
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