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The principle is simple: as we walk, we waste energy that could be harvested. A group of US researchers took that concept on board and developed a way to generate electricity from human motion. They created a device that could be placed in a shoe in order to capture the energy of moving micro droplets, converting it into electrical current.

The team from the University of Wisconsin published their study in the journal Nature Communications and Professor Tom Krupenkin from the institution’s mechanical engineering department explained their invention: “Humans are very powerful energy-producing machines. While sprinting, a person can produce as much as a Kilowatt of power.” And a Kilowatt is more than enough to power a standard mobile phone. 

Until now, the problem was the lack of a practical mechanism which would allow the conversion of that power into electricity, providing the required output. “What’s been missing is the power in the watts range” explained Krupenkin “That’s the power range needed for portable electronics.”

Industrial scale devices have been in use, but are not adequate for individual use. An example is the power-generating mats installed under the floors at two Tokyo train stations, designed to capture the vibrations of thousands of commuters. Their energy is being used to power several appliances, including the stations’ automatic doors. 

The new mechanism for personal use is somewhat different: it uses a principle known as ‘reverse electrowetting’ or – put another way- it converts the energy of moving microscopic liquid droplets into an electrical current. The device is fitted in a shoe and getting the energy from it is on itself another challenge – one could always do it by plugging a USB cable into the shoe (which would look a bit outlandish), but the University of Wisconsin team has a more sleek solution that doesn’t involve any visible cables coming out of shoes.

The team’s solution is to have the electricity-generating mechanism connected to a shoe-bound wireless transmitter. Signals could be passed between the unit and the handset through Bluetooth or wi-fi, solving the problem of unsightly cables.