It’s electric! Harvesting energy from body movement?

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Frank Wojciechowski Photo Courtesy of the American Chemical Society

As my colleague Bryan Walsh reported back in 2008, wind farms and solar panels aren’t the only places that scientists have been looking for some extra electricity. From knee braces that tap into the energy in a person’s stride to vibration harvesters that soak up energy from the buzz of a busy highway, researchers are hard at work coming up with little ways to plug into the world around us, so to speak. And a new development reported this week in the American Chemical Society journal Nano Letters may go some distance toward achieving that—and even harvesting enough electricity to power small devices like cell phones or even pacemakers.

Integrating “highly efficient energy conversion materials” onto thin, stretchy sections of bio-compatible rubber to create a new material known as “piezo-rubber” may be the way forward to designing “wearable energy harvesting systems,” according to the team of engineers from Princeton University and the California Institute of Technology. Incorporating materials that generate electricity when they are flexed or put under pressure—or piezoelectric materials, as they are known in engineering circles—into thin strips of rubber has been a particularly big challenge as manufacturing those materials requires very high temperatures (upwards of 1000ºF), in which the rubber wouldn’t fare so well.

Yet, this entourage of engineers—from specialties in electronics to chemistry and mechanics—were up to the challenge. In a novel manufacturing technique, they were able to apply the tiniest threads of the piezoelectric material lead zirconate titanate (strands of which were about 1/50,000th the width of a human hair) into thin pieces of silicone rubber. Known as PZT, lead zirconate titanate is one of the most efficient piezoelectric materials—able to convert 80% of mechanical energy into electricity.

That is particularly promising considering the surplus of energy all around us, the study’s authors point out. “[T]he heel strike during walking is a particularly rich source of energy with 67 [watts] of power available from a brisk walker. Harvesting even 1−5% of that power would be sufficient to run many body-worn devices such as mobile phones.”

The technology could have promising uses in medicine as well, they suggest. “Lung motion by breathing can generate up to 1 W of power. If this power were harvested into charging a pacemaker battery, it may increase the time required between battery replacement surgeries for patients.”

There are still hurdles to using this technology in everyday life—such as gaining a better understanding of how the piezoelectric materials will perform on stretchy platforms—but this new technique represents an important step toward toward the “implementation of wearable or even implantable energy harvesters, and biological force sensing microdevices,” the engineers conclude.