Photo: Flickr/[email protected]
Turning the human body into a power station sounds like a zany plotline from the Matrix movies, but scientists are starting to take seriously the idea that one way to stem climate change might be to harvest tiny amounts of energy in the form of the body’s heat, movement, metabolism and vibrations.In one form of the technology, experts are turning to piezoelectricity, which means “electricity resulting from pressure”. In a piezoelectric material, small amounts of power are generated when it is pushed out of shape. As an extraordinary example of what’s now possible with these materials, the heart itself could be used to power an artificial pacemaker. Though these devices require only tiny amounts of power – one millionth of a watt – their batteries typically run out after a few years. But as Dr Amin Karami at the University of Michigan says, a pacemaker that harvests the energy of the heartbeat itself might operate for a lifetime. In a recent address to the American Heart Association in Los Angeles, he pointed out that a sliver of a piezoelectric ceramic one hundredth of an inch thick, powered by vibrations in the chest cavity, is able to generate almost 10 times the power required to operate a pacemaker.
The technology can be used on the outside of the body as well. Nanotechnology researchers are developing the perfect complement to the power tie: a “power shirt” woven from pairs of fibres coated with tiny strips of zinc oxide and gold. As you move, the fibres rub against each other to produce a current. Prof Zhong Lin Wang, at the Georgia Institute of Technology, says that “we could provide a flexible, foldable and wearable power source that, for example, would allow people to generate their own electrical current while walking”.
In Britain, at the University of Newcastle, Dr Michele Pozzi has created a “pizzicato” energy source that could power a satellite navigation device. Fixed on the knee, the device consists of an outer ring and central hub. As you walk, the ring rotates, and 72 plectra around it “pluck” four piezoelectric arms on the hub, generating electricity. Steve Burrows, of Bristol University, has harnessed the up-and-down motion of walking to turn an electricity generator. Even our footsteps can generate power, by driving a salty liquid through microscopic pores in a shoe sole to deliver up to two watts per leg, using a “reverse electrowetting” device developed by Prof Tom Krupenkin at the University of Wisconsin, Madison. “This is more than sufficient to power such common devices as smartphones and tablets,” he says. “We expect the first product prototype to be available in one to two years.”
Laurie Winkless, of the National Physical Laboratory in Teddington, has studied a range of such harvesting technologies. She points out that they have their drawbacks. A piezoelectric “battery” inside a heel may be able to power emergency location devices for hikers, but the wearer will feel the added resistance from anything above a few tenths of a watt. There are also problems with so-called “thermoelectric” materials, which generate electricity when one side is hot and the other cold: a shirt made of such a fabric could draw too much heat from the body, leaving the wearer feeling chilly.
Overall, however, the future for such nanogeneration appears bright. In the Science Museum’s Atmosphere gallery, we have a model of one promising technology that is now in use: a paving slab made by Pavegen Systems to scavenge the energy of tramping feet. The company’s tiles were incorporated in a walkway leading to the Olympic Park that turned more than 10 million footsteps into enough energy to illuminate the walkway for eight hours each day.
In future, says Winkless, a range of energy-grubbing technologies will increasingly appear in the home: “Energy harvesting pots could mean that boiling your pasta charges your mobile phone. The vibrations of your washing machine could power wireless sensors – or your TV remote could be powered just by you pressing the buttons.”
Roger Highfield is director of external affairs at the Science Museum Group
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