Phones could be powered by user's body heat

Dead cellphones could soon be a thing of the past, thanks to a new technology that can harvest enough juice for another call from the user's own body heat. Developed by researchers in the Center for Nanotechnology and Molecular Materials at Wake Forest University, Power Felt is based on tiny carbon nanotubes encased in flexible plastic fibers and uses temperature differences – room temperature versus body temperature, for instance – to create a charge.

"We waste a lot of energy in the form of heat. For example, recapturing a car's energy waste could help improve fuel mileage and power the radio, air conditioning or navigation system," says graduate student Corey Hewitt

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"Generally thermoelectrics are an underdeveloped technology for harvesting energy, yet there is so much opportunity."

Potential uses for Power Felt include lining automobile seats to boost battery power and service electrical needs, insulating pipes or collecting heat under roof tiles to lower gas or electric bills.

It could also be used to lineclothing or sports equipment to monitor performance, or to wrap IV or wound sites to better track patients' medical needs.

"Imagine it in an emergency kit, wrapped around a flashlight, powering a weather radio, charging a prepaid cell phone," says David Carroll, director of the Center for Nanotechnology and Molecular Materials. "Power Felt could provide relief during power outages or accidents."

The reason thermoelectrics haven't been used more widely in the past is simple - cost. Standard thermoelectric devices use a much more efficient compound called bismuth telluride to turn heat into power in products including mobile refrigerators and CPU coolers, but  can cost $1,000 per kilogram.

But the Wake researchers are confident that, in bulk, their system could costs as little as $1 to add to a cellphone cover.

Currently, 72 stacked layers in the fabric yield about 140 nanowatts of power. The team is evaluating several ways to add more nanotube layers and make them even thinner to boost the power output.

There's more work to do, but Wake Forest says it's in talks with investors to produce Power Felt commercially.