Recharging batteries now a walkover

One day soon, you may be able to charge your mobile phone simply by walking.

A team of professors has invented a tiny rubber device that converts the energy generated from body movements into an electric current.

Michael McAlpine, the professor at America's Princeton University who led the effort, said that it could one day replace batteries for pacemakers, phones and other gadgets.

"It is about capturing waste power that is generated through everyday motion," he said. "In the short term, if we can marry this technology to batteries, then the least we can hope to do is extend the life of batteries. Eventually, they could be replaced entirely."

The device is made of tiny ribbons of ceramic material called lead zirconate titanate (PZT) that is "piezoelectric", which means it produces an electric current when flexed. The word is derived from the Greek "piezo" or "piezein", which means to squeeze or press.

The strips are so narrow, 100 of them can fit in a millimetre. The ribbons are encased in silicone rubber sheets which could be placed inside the chest cavity, for example, to generate power for a pacemaker as the ribcage rises and falls.

Said McAlpine: "The crystals have lead in them so we had to make them bio-compatible for the human body by applying a material like silicone, which we know the body accepts because it is used for cosmetic implants and medical devices."

The Ivy League university's research was funded by the US Intelligence Community, a co-operative of the federal intelligence and national security agencies. It was intended to power the tiny wings of spy drones built to look like dragonflies.

"In the same way that it generates electricity when it is flexed, the reverse is true: the material flexes when an electric current is applied to it. This is how we started out, but it opens the door to other kinds of applications," said McAlpine.

He hopes to license the technology to a multinational that could incorporate it into a range of products. At the moment, the most the strips can generate is 10mW, enough to power the LED lights in children's trainers.

With more research, they hope to get it up to 1W, which would be sufficient to power a mobile phone, an iPod or a pacemaker. "The power generated depends on the size of the chip we can produce," said McAlpine. "As we get better at making these chips, we will be able to make larger and larger sheets."