Watt Next? More Power To Your Elbow

Sydney Morning Herald

Saturday February 9, 2008

Deborah Smith Science Editor

POWER walking is set to take on a new meaning, with the development of a knee brace that could make charging a mobile phone as easy as strolling around the block.

It harvests energy from the knee as it straightens after a stride. Two devices worn together can generate about five watts of electrical power - enough to run 10 phones at the same time - with little extra effort by the wearer, a study has shown.

The bright idea by an American and Canadian team is the latest advance in a scientific bid to make people power a source of ready energy.

A spring-loaded backpack that generates electricity as it bounces up and down with its wearer has also been designed in the US. And the CSIRO was recently awarded a $4.4 million Defence Department grant to develop a jacket made of fabric that harvests energy from the vibrations as people move.

Tony Hollenkamp, of CSIRO Energy Technology, said the plan was for this human-produced electrical energy to be stored in flexible batteries in the jacket or to power plug-in devices like a GPS, phone, computer, or light.

While the jacket would have important defence applications, allowing soldiers with high-tech equipment to stay longer in the field under their own steam, others would find it an attractive option, Dr Hollenkamp predicted.

"I can imagine someone hiking in the bush who wants to take a few mod cons, like a GPS, would want to use it. The only other option is strapping a big battery to your back."

People have long relied on their own energy to crank, squeeze, wind up, spin, pump, push and pull devices into action. But using everyday human movement as a power source has required the development of sophisticated electronics, Dr Hollenkamp said.

Arthur Kuo, of the University of Michigan, a member of the team that developed the knee brace, said the human body was clever. Rather than dissipating energy as it moved, it stored it in many places, such as in springy tendons. But "we believe that when you're slowing down the knee at the end of swinging the leg, most of that energy normally is just wasted".

The knee device taps into this energy in the same way hybrid-electric cars recycle power from braking, said Dr Kuo, whose study is published in Science.

Half a billion children in the world live without electricity and the simple knee device might eventually help them power computers, the team said.

However, the 1.6 kilogram prototype was bulky and needed refinement.

TURN ME ON

BACKPACK

Spring-loaded backpack harnesses up and down motions. A 38kg load generates 7.4 watts during fast walking.

JACKET

Under development by CSIRO. Generates electricity from vibrations and stores it in flexible batteries.

KNEE

Harvests energy lost when knee brakes after taking a step.

A pair of the 1.6kg prototypes generate about five watts of electricity.

SOURCE: SCIENCE, CSIRO

© 2008 Sydney Morning Herald

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