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Human Gait to Power Portable Electronics

Engineering researchers Tom Krupenkin and J. Ashley Taylor at the University of Wisconsin-Madison have developed a new energy-harvesting technology that could reduce our dependence on batteries and instead capture the energy of human motion to power portable electronics.

"Humans, generally speaking, are very powerful energy-producing machines," explains Krupenkin, a UW-Madison professor of mechanical engineering. "While sprinting, a person can produce as much as a kilowatt of power."

Taking even a small fraction of that energy is enough to power a host of mobile electronic devices. Current energy harvesting technologies are aimed at either high-power applications such as wind or solar power, or low-power applications like calculators or sensors. "What's been missing," says Taylor, "is the power in the watts range. That's the power range needed for portable electronics."

The researchers discovered a novel energy-harvesting technology known as "reverse electrowetting." The mechanical energy is converted to electrical energy by using a micro-fluidic device consisting of thousands of liquid micro-droplets interacting with a novel nano-structured substrate.


This technology could enable a novel footwear-embedded energy harvester that captures energy produced by humans during walking, which is normally lost as heat, and converts it into up to 20 watts of electrical power that can be used to power mobile electronic devices. Unlike a traditional battery, the energy harvester never needs to be recharged, as the new energy is constantly generated during the normal walking process.

Taylor and Krupenkin were inspired by limitations that current battery technology imposes on mobile electronics users. The energy generated by the footwear-embedded harvester can be used in one of two ways. It can be used directly to power a broad range of devices, from smartphones and laptops to radios, GPS units, and flashlights.

Alternatively, the energy harvester can be integrated with a Wi-Fi hot spot that acts as a middleman between mobile devices and a wireless network. This allows users to seamlessly utilize the energy generated by the harvester without having to physically connect their mobile devices to the footwear. Such a configuration dramatically reduces power consumption of wireless mobile devices and allows them to operate for much longer time without battery recharge.

Even though energy harvesting is unlikely to completely replace batteries in the majority of mobile applications, the researchers believe it can play a key role in reducing cost, pollution, and other problems associated with battery use. The hope, they say, is that the novel mechanical to electrical energy conversion process they pioneered can go a long way toward achieving that goal.

(University of Wisconsin-Madison)