Using every step to help recharge smartphones or iPods has not yet become reality, but scientists are working on it. Their latest solution converts the energy from human motion into electricity by harnessing thousands of tiny liquid droplets inside a micro-fluidic device.
If embedded in footwear, the energy-harvesting device may help gadgets such as laptop computers and cell phones run for longer on their existing batteries. U.S. soldiers could wear the device to help power their radios, GPS units and night-vision goggles and perhaps lighten existing loads of as much as 20 pounds of batteries.
It may even work with Wi-Fi hot spots in cafes or parks to act as the middleman between mobile devices and wireless networks — a configuration that can allow wireless mobile devices to go for much longer without a recharge.
"You cut the power requirements of your cellphone dramatically by doing this," said Tom Krupenkin, a mechanical engineer at the University of Wisconsin-Madison. "Your cellphone battery will last 10 times longer."
Existing energy harvesters aim to help either high-power applications such as wind or solar power, or very low-power applications on the level of watches or tiny sensors. The new energy-harvester can fill the gap in the watts range for portable electronic devices, said J. Ashley Taylor, a mechanical engineer at the University of Wisconsin-Madison.
A person who wears the energy harvester while walking can generate up to 20 watts of electrical power. That's enough to help power mobile electronic devices ranging from laptop computers to cell phones and keep them running for longer without worrying about plugging into a power socket.
"Humans, generally speaking, are very powerful energy-producing machines," Krupenkin said. "While sprinting, a person can produce as much as a kilowatt of power."
The researchers hope to commercialize the technology with their new startup, InStep NanoPower. A paper about the work appears in the week Aug. 23 issue of the journal Nature Communications.