Power walk – harnessing energy from everyday movements

These boots are made for walking . . . and for powering up your cell phone?
It could happen, according to a team of Princeton and Caltech scientists. In a recent paper in the journal Nano Letters, they report that they have developed an innovative rubber chip that has the ability to harvest energy from motions such as walking, running, and breathing and convert it into a power source.
Score one for the body electric.

“It opens up a lot of possibilities,” says Caltech graduate student Habib Ahmad, a coauthor on the paper. “We all dissipate energy as we move our bodies around, and conceivably that energy could be put to work charging small electronic devices like an iPod or a cell phone.”

The piezoelectric ribbons covering this minuscule rubber chip have the capacity to harness energy generated from body motions.
The key to this development is a class of materials known as piezoelectrics, which are substances—chiefly crystalline and ceramic—that respond to stress or strain by producing a charge, essentially converting mechanical energy to electrical energy. (“Piezo” derives from a Greek word, meaning to squeeze or exert pressure.)
“Piezoelectrics have been around for a while,” says Ahmad. “The best-known and most widely used natural one is quartz.” Ceramic ones, many of them man-made, often produce more voltage when stressed, but keeping that voltage level high generally requires that they be grown on a hard surface, or substrate. That limits how flexibly they can respond to the pressure generated by, say, a swinging arm or a treading foot.
Ahmad is currently working toward his PhD in the lab of Caltech’s Gilloon Professor and Professor of Chemistry James Heath, where he is developing micro- and nanodevices—ultrasmall instruments—that can aid in detecting and diagnosing certain types of cancer. He got involved in a precursor to the piezoelectric research a couple of years ago when he collaborated with Heath postdoc Michael McAlpine in testing out a new technique that McAlpine had come up with for transferring silicon nanowires from an inflexible substrate to a plastic one.



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