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David Carroll Turns Fabric Into an Energy Source

This high-powered microscope can see the nanotubes in Power Felt

Taj Forer for Bloomberg Businessweek

This high-powered microscope can see the nanotubes in Power Felt

The women in David Carroll’s life are big talkers, and that takes a toll on his cell phone battery. “My wife likes to call me, and she does take her time when she tells her stories,” he says. “You can watch the power meter just go down.” Carroll, a physicist and head of Wake Forest University’s Center for Nanotechnology and Molecular Materials, was discussing this problem last year with his 10-year-old daughter, Lauren, when she came up with a suggestion: What if Carroll could design something that harnessed the heat from someone’s hand, or from the phone itself, to give a cell phone battery more power? Carroll agreed that would be pretty cool.

Last month, Carroll’s lab unveiled a fabric that does just that. Called Power Felt, it generates electricity from heat. Wrap your cell phone in Power Felt, and it feeds off your body heat to recharge while it’s in your pocket. Carroll is a lifelong Southerner—he’s descended from some of North Carolina’s first white settlers, and his family donated some of the land that Wake Forest sits on—and he’s acutely aware of how powerful summer heat can be. He says Power Felt installed just under the roof of a house could be used to power household appliances. Lay it on the floor of a car and it could use the heat generated from sitting in a midday parking lot to run air conditioning and the radio. In an electric or a hybrid car, the Power Felt might even boost mileage.

The challenge for his team, says Carroll, was to create something that was electrically conductive—the way metal is—and thermally insulating—the way cloth can be. The solution was to imprint carbon nanotubes onto a woven mat of plastic fibers. Since it takes relatively few carbon nanotubes to give the fabric thermoelectric properties, the cost is reasonable. Carroll estimates that, at a large scale, Power Felt could be fabricated for as little as a dollar for a swatch big enough to cover a cell phone.

Carroll says he is in talks with more than 20 potential investors and collaborators—the defense and aerospace company Thales among them. Carl Batt, co-founder of Cornell University’s Nanobiotechnology Center, calls Carroll’s felt “an interesting approach” to generating power. “It’s a relatively untapped field.”

Fabrics have been one area in which the sometimes hyperbolic claims made for nanotechnology are being borne out. Engineers have been able to use nanopores and nanowhiskers—tiny holes and strands as thin as a single molecule—to make fabrics that kill bacteria and protect against hazardous chemicals.

Carroll believes Power Felt could fuel sensors worn on the body, perhaps embedded in clothing, that would allow doctors to keep track of patients’ health remotely. And wrapping consumer electronics in Power Felt, Carroll notes, is far cheaper than upgrading their batteries. “While I’ve been talking to you, the back of my phone has gotten hot,” he says. “Our $1 piece of fabric would give you the same amount of boost as a $50 battery would.”


His 11-year-old daughter and her friends


Power Felt, which generates electricity from heat

Spare time

Plays bagpipes and classical guitar

Bennett is a staff writer for Bloomberg Businessweek in New York.

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