In the "Back to the Future" movies, Marty McFly travels to the year 2015 and finds himself overwhelmed by futuristic technology, such as flying cars, hoverboards and self-lacing shoes. Well, it's now 2015, and we don't have any practical flying cars or hoverboards — But we might soon have self-lacing shoes, reports the BBC

German researchers have built electronic devices for shoes that can be powered by walking, with the ultimate aim of designing shoes that lace themselves without any need for batteries. The shoes will help the elderly keep their laces tied without having to bend over or struggle with the laces — but they'll also be pretty cool for people of all ages who fancy the go-go-gadget design.

The shoe works thanks to two separate devices, a "shock harvester" that generates power when the heel strikes the ground and a "swing harvester" that produces power when the foot is swinging. Both devices exploit the motion between magnets and coils to generate power. The energy generated by the prototypes is still relatively small, in the three to four milliWatt (mW) range, so they can't be used to charge gluttonous energy hogs like smartphones, but they can power small sensors and transmitters. 

Power output is limited by size and weight of the shoe — there's little use for an electronic shoe that is cumbersome to wear. So the devices represent a trade-off between power generation and size, but researchers are optimistic that future designs can be made that generate even more power.

"Generated power scales with size, but if you want to be able to reasonably integrate such a device within a shoe sole, you have to work with strict constraints, like a small height and limited length of the device," Klevis Ylli, one of the designers of the shoe, told BBC News. "We believe we have built comparatively small devices, considering the power output."

Powered laces won't be the only futuristic function for the shoes. Data about walking speed, location and direction of travel can also be generated and transmitted wirelessly.

"One application we are working on is indoor navigation which means we have sensors within the shoe that measure the acceleration of the foot, the angular velocity - whether you're turning the foot or not - and the magnetic field," explained Ylli. "From the data from these sensors, you could calculate how far you have travelled and in which direction. So imagine a rescue unit walking into a building they don't know. They could then track which way they went on their handheld device."

The shoes could not only be useful for rescue units, but also for those interested in tracking their fitness. Perhaps in the future such tracking devices could also be used to help correct a person's gait.

The most immediate goal, though, is to make them the world's first practical self-lacing shoes. If they catch on, learning how to tie one's shoes may become an antiquated rite of passage. But perhaps the cost in nostalgia will be worth it if it means we're one step closer to realizing the 2015 imagined in "Back to the Future."

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