Alternative Power

For years, researchers have longed to discover a better way to power small mobile devices, such as personal portable electronics, small sensors (such as implantable biosensors to monitor diabetics’ glucose levels), micromechanical systems (MEMS), and military/homeland security electronics. Batteries have, of course, been the traditional mobile power source of choice, since they can convert up to about 75 percent of the potential energy they contain into electrical current.

 

Fuel cells using methyl alcohol (more popularly known as methanol or wood alcohol) have often been mentioned as a possible replacement for batteries, since Direct Methanol Fuel Cells (DMFCs) offer some advantages over lithium-ion batteries, such as a longer runtime between charges over today’s battery technologies, and a fast “refill” of methanol as opposed to a lengthy recharge of a battery. But even the best among these can extract only about 60 percent of energy available in the fuel they use and fuel cells small enough to embed within mobile devices are even less efficient.

 

Now, however, scientists in the U.S. have developed tiny brush-like fibers that generate electrical energy from movement, suggesting that clothes could be produced capable of harnessing the energy generated by movements of the human body.

 

The idea goes back to the 1920s, when watchmakers first came upon the idea of the self-winding wristwatch, a device powered by harvesting the mechanical energy from a user’s moving arm. Today’s “nanogenerators” are composed of tiny sets of fiber pairs having Kevlar cores. They are bathed in a solution that causes many amazingly tiny (30 to 50 nanometers, or billionths of a meter) “nanowires” made of zinc oxide to grow and bristle out radially from the surface of each fiber. Zinc oxide is unusual in that it has both piezoelectric and semiconducting properties, which means that moving them generates electrical energy. In each fiber pair, one fiber is coated with gold to act as an electrode that gathers and conducts the electricity that’s generated by the fabric’s movements.

 

Experiments indicate that two one-centimeter-long fibers can generate a current of four nanoamperes and an output voltage of about four millivolts. It’s believed that an optimized version of this could deliver 80 milliwatts per square meter of fabric ­— enough to power an iPod.

 

Writing in the scientific journal Nature, the scientists, including Professor Zhong Lin Wang of the Georgia Institute of Technology (News - Alert), claim the fiber could be used in tents or other larger structures to harness wind energy. But, to produce higher voltages, a way must be devised to make nanowires of identical height and diameter.

 

When the process is perfected, companies such as Fibretronic will be ready. The company makes “soft” electronic component solutions, such as textile-based switches and keypads, fabric iPod controls, wearable sensor and lighting systems, and other soft-format electronics available for application in a range of textile and related products. With Fibretronic technology, users, for example, can control mp3 players in their pockets. Woolrich, which has been making Parka jackets since 1830, has incorporated Fibretronic’s iPod keypad controller into the sleeve of their “I-Military” jacket. The men’s Cordura jacket is now on sale in Woolrich stores in Europe.

 

The U.S. Defense Advanced Research Projects agency DARPA, is also looking into ways to harvest otherwise lost energy from soldiers in the field to power devices, such as an electricity-generating pair of boots.

 

The common joke circulating about power fibers is that they give a whole new meaning to the term “power dressing.”