Energy scavengers power gadget-obsessed world

The world is learning to scavenge for leftover energy. Max Donelan of Simon Fraser University in Vancouver, Canada has adapted a prosthetic knee brace to generate electricity from the wearer's leg movements as they walk. With one on each knee, the braces can generate enough electricity to top up the battery on a mobile phone or MP3 Player.

It's just one of a number of so-called 'energy harvesting' technologies in development.

The brace doesn't impede the wearer in any way. In fact, through a novel clutch mechanism, it actually aids walking by engaging only in the phase of the gait just before footfall where the knee acts as a brake. By tapping in to this 'negative energy', the brace harvests power that would otherwise be wasted.

At Perpetuum, a spin-out company of the University of Southampton, the focus is on converting barely perceptible vibrations into

useful energy. A cylindrical energy-harvesting device about the size of a drinks can sits on the side of a motor. The spinning of the motor is sufficient for the device to generate enough electricity to power a built-in sensor that gauges the frequency at which the motor is vibrating.

The sensor sporadically transmits data about the motor's vibrations to a wireless receiver a few hundred metres away. The concept is perfect for keeping an eye on large industrial plants where machinery would otherwise need to be monitored by battery-powered devices.

Another setting where replacing batteries is expensive and disruptive is in pacemakers implanted into the body. At Imperial College London, engineers are working on a unit sensitive enough to harvest energy from the metronomic beating of the heart. It generates just enough power to top up the battery on a pacemaker. So, the device that keeps the heart beating is assisted by energy generated from the heart itself. Perfect.
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