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Research aims to harness human motion energy

Posted: 25 Aug 2011 ?? ?Print Version ?Bookmark and Share

Keywords:energy harvesting technology? human motion? portable device? mobile electronics?

Various energy harvesting technologies are delving into either high-power applications such as solar or wind, or very low-power devices such as calculators and watches. However, two engineering researchers from the University of Wisconsin-Madison are looking into a new energy-harvesting technology: human motion.

If the technology to capture the energy of human motion could be completed, people may no longer depend on batteries to power portable electronics. "Humans, generally speaking, are very powerful energy-producing machines," explained Tom Krupenkin, a UW-Madison professor of mechanical engineering. "While sprinting, a person can produce as much as a kilowatt of power."

Grabbing even a small fraction of that energy is enough to power a host of mobile electronic deviceseverything from laptops to cellphones to flashlights, added Krupenkin. "What has been lacking is a mechanical-to-electrical energy conversion technology that would work well for this type of application."

Solar power can also be used to power portable electronics, but, unlike human motion, direct sunlight is usually not a readily available source of energy for mobile electronics users. "What's been missing is the power in the watts range. That's the power range needed for portable electronics," stated J. Ashley Taylor, researcher, UW-Madison.

Krupenkin and Taylor have described what they discovered as 'reverse electrowetting' in which 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 footwear-embedded energy harvester to capture energy produced by humans during walking that is normally lost as heat. It can convert that energy into at most 20W of electrical power that can power mobile electronic devices. Unlike a traditional battery, the energy harvester never needs to be recharged as the new energy is constantly generated when walking.

The initial development of this technology was funded by a National Science Foundation Small Business Innovation Research grant. Now Krupenkin and Taylor are seeking to commercialize the technology through a company they have established, InStep NanoPower.

In their work, Taylor and Krupenkin were inspired by severe limitations that current battery technology imposes on mobile electronics users. As any cellphone or laptop user knows, heavy reliance on batteries greatly restricts the utility of mobile electronic devices in many situations. What's more, many mobile electronics are used in remote areas where electrical grids for recharging batteries are often not available. Cellphone users in developing countries often have to pay high fees to have cellphones charged. Similar problems face military and law enforcement personnel. Soldiers, for example, head into the field carrying as much as 20lbs of batteries to power communications equipment, laptops and night-vision goggles.

The energy generated by the footwear-embedded harvester can be used in two ways. It can directly power a range of devices such as smartphones and radios, or it can be integrated with a WiFi hotspot that acts as a 'middleman' between mobile devices and a wireless network. This allows users to use 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, the researchers said.

"You cut the power requirements of your cellphone dramatically by doing this. Your cellphone battery will last 10 times longer," claimed Krupenkin.

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 is that the novel mechanical to electrical energy conversion process they pioneered can go a long way toward achieving that goal.

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