Power-generating device could be embedded in footwear

In a paper appearing today in the journal Nature Communications, Tom Krupenkin and J Ashley Taylor describe a new energy-harvesting technology that captures the energy of human motion to power portable electronics.

‘Humans, generally speaking, are very powerful energy-producing machines,’ said Krupenkin, a University of Wisconsin-Madison professor of mechanical engineering. ‘While sprinting, a person can produce as much as a kilowatt of power.’

Exploiting a small fraction of that energy, Krupenkin said, is enough to power a host of mobile electronic devices, including laptop computers, cell phones and flashlights.

‘What has been lacking is a mechanical-to-electrical energy conversion technology that would work well for this type of application,’ he said.

According to the university, current energy-harvesting technologies are aimed at either high-power applications, such as wind or solar power, or very low-power applications, such as calculators, watches or sensors. ‘What’s been missing is the power in the watts range,’ said Taylor, an engineering researcher at the University of Wisconsin-Madison. ‘That’s the power range needed for portable electronics.’

Solar power, the researchers said, 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.

In their report, Krupenkin and Taylor described 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.

It is claimed that 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 20W of electrical power. Unlike a traditional battery, the energy harvester doesn’t need to be recharged, as the new energy is constantly generated during the normal walking process.

The energy generated by the footwear-embedded harvester can be used in one of two ways. First, it can be used directly to power a broad range of devices, from smartphones and laptops to radios, GPS units, night-vision goggles and flashlights.

Alternatively, the energy harvester can be integrated with a Wi-Fi hot spot that acts as a ‘middle man’ between mobile devices and a wireless network. This allows users to utilise the energy generated by the harvester without having to physically connect their mobile devices to the footwear. Such a configuration reduces power consumption of wireless mobile devices and allows them to operate for much longer without battery recharge, the Wisconsin researchers said.

Krupenkin and Taylor have established InStep NanoPower in order to commercialise the technology.