Clothes that generate electric power

“Someday we’ll all be wearing clothing that generates electricity.” (…not just static) This statement or something comparable appears in a science or technology story at least a couple of times a year. The broad implication is that by some (new) technology, the motions of daily life will cause our clothing to generate electricity, which can be used to run small electronics (radios, watches, computers, cell phones). It’s true. It probably will happen; but perhaps we shouldn’t get hung up on this kind of clothing…

There’s a whiff of science fiction in the idea of clothes that power your watch, or iPod, or even pacemaker. However, the prototypes are already being stitched together. A quick search will turn up more examples than you’d care to try on for size (2003-Italy, 2007-Australia, 2008-Georgia, USA, 2009-USA, 2010-Berkeley, USA), the common thread through them all is the use of piezoelectricity. This is the ability of some materials to generate an electric field in response to mechanical stress – that is, bending. It the material is suitable, it can be cut and shaped to fit (somewhere) on the human body – typically shoes, shirts, belts (belts?) – that bends or twists with normal body movement.

As you might guess, the current generated by this kind of piezoelectric material isn’t very strong, typically measured in millivolts and nanoamps; but it’s not negligible. If there is some way to store and concentrate the energy generated while moving (so it’s also available when not moving), then there’s a way for piezoelectrics to be incorporated in articles of clothing and service small electronics.

There are several recent (2010) versions already:

Princeton University (New Jersey, USA) and CalTech (California, USA) have published a version that prints piezoelectric ribbons on rubber, which can then be incorporated into clothing, shoes, and the like. [Source: ACS Nanoletters]

Cornell University (New York, USA) in the laboratory of Juan Hinestroza, has developed cotton threads coated with electrically conductive nanoparticles. This material doesn’t generate the electricity, but can easily be hooked to flexible solar plates (somewhere on the body) to transfer the electricity. The apparent advantage of this approach is the material remains more like material and less like a plastic sheet (or some other marginally pliable material). [Source: EurekAlert]

The University of California Berkeley has developed nanofibers made from organic polyvinylidene fluoride (PVD), which is flexible and inexpensive to manufacture. The nanofibers respond to tugging or stretching to generate electricity. One of the contributions of the research was a technique that aligns the polymeric nanogenerators (how’s that for a cocktail party phrase?) 50 micrometers apart in a grid pattern. This makes it easier to control the placement of fibers, and more importantly to align the positive and negative ends of the fibers so they don’t cancel each other out. The fibers are essentially nanosize – so small that they wouldn’t be woven into fabric but perhaps mixed into a fabric almost like a coating. This particular method is apparently one of the most efficient yet developed. [Source: University of California Berkeley]

From all this activity, you’d think there’s a major demand for electrified clothing. Of course not; how could there be? Outside of a few prototypes, nobody’s worn an electric generating piece of clothing. It’s one of those pieces of technology that probably won’t find its killer app (don’t take that too literally) until the material is ready for commercial application. The simple, ‘well, it can provide free power to recharge your cell phone’ sounds good, but might not be enough to push the idea into the mainstream.

There are a few practical questions:

How will it last multiple washings with strong detergents?
Does it have anything that will eventually weaken with bending?
What can tears or holes do to the material’s electrical ability?
Is it comfortable to wear?
Will any of the ingredients cause allergic reactions?
For that matter, what will an electric field in clothing do to the body?
What will it cost? (Especially relative to battery technology.)
Does it also need (costly, ungainly) batteries to store the energy?

There are no doubt answers to all these questions, but not necessarily in a nice neat package. The ‘ideal’ approach to electricity generating clothing may not have been discovered yet. Nevertheless, this is the kind of technology on which new industries can be founded – as long as the technology becomes good, cheap, and flexible.

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