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.
From the standpoint of thermal dynamics, I would assume that since the fabric produced electricity it also causes the cool side to warm up and the warm side to cool down. So if I as a consumer buy a coat made of this fabric to stay warm and charge my phone with it. Since the warm side is being cooled, will the coat be able to keep me warm?
On heat transfer:This material is converting the energy (temperature) differential to another form of energy differential (electrical potential, or Voltage), which creates electrical current.I would believe that this would not change the heat storage characteristics of the coat, etc., significantly for two reasons:
1.Entropy:The material is not "creating" energy, but routing it.
2.Magnitude:We're probably talking microAmperes, or at best milliAmperes – probably not a significant enough energy exchange to be felt...
This whole concept sounds like a great idea to me - in our low-power device world - if applied well and if efficiencies can make it up to a useful level.
On ESD (electrostatic discharge): I would not think such a material would build a static field charge, but rather dissipate it (or maybe even USE it?).
Mydesign, I think you have a good point. The power crunch in portables is extreme enough that a combination of walking- and non-walking-activated methods may well be needed.
vimalkumarp, that sounds like a really interesting energy harvesting application you describe. Can you tell us anything about how it works, or are the details under wraps right now?
Ann, that is my PhD thesis. I am planning to use Energymicro lowpower processor and energy harvesting from Linear technology. I will update you as I progress. my mail id is perec.vimal@gmail.com . Please do give me your mail id so that i can send you my review paper and also synopsis if you are interested to read. i am trying to explore the possiblilies of energy harvesting for SHM for aricrafts
I am a biomedical engineer and i am keen to explore this in vital parameters monitoring too. Do enlighten me about your ideas so that i know more about energy harvesting. I will update you about my PhD as time progresses.
energy harvesting is excellent idea but one important aspect is that the design should consume less power. This is how an energy harvesting application can complement or vice versa a low power consuming design.
Thanks for the reply, vimalkumarp. My area of coverage for DN is materials, not energy harvesting per se, which is why I wrote about the Power Felt fabric. Several of us DN editors report on energy harvesting and SHM (although none of us are experts) and I'm especially interested in materials that aid SHM for aircraft. I've passed on your contact info to my colleagues. In any case, please do let us know when you are done with the thesis and have your results.
Vimalkumarp: Here are a couple of previous stories we did about energy harvesting, with a little bit of info about using temperature gradients as a source:
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