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Wearable Device Generates Electricity From Walking Knee Movements
Zothecula writes "If you've ever worn a knee brace, then you may have noticed what a large change in angle your knee goes through with every step you take, and how quickly it does so. A team of scientists from the U.K.'s Cranfield University, University of Liverpool and University of Salford certainly noticed, and decided that all that movement should be put to use. The result is a wearable piezoelectric device that converts knee movement into electricity, which could in turn be used to power gadgets such as heart rate monitors, pedometers and accelerometers."
Quick comparison with a regular AA battery... they are usually around 2000mAh, 1.5V, or about 3Wh energy. So about 1500 hours of constant knee movement at 2mW. Assuming a generous 4 hours/day of walking, this generates the equivalent of a single AA cell every year. Meh.
"I bless every day that I continue to live, for every day is pure profit."
I was thinking more along the lines of the stillsuit, which if I recall correctly was powered in via movement.
Walking is a very low-energy form of movement that relies on some highly evolved bio-mechnics. Attempting to harvest a useful amount of energy introduces dissipation in parts of the 'mechanism' that have not evolved to handle it. The result can be anything from mild discomfort to quite serious injuries. So, such techniques are limited to a few mW, and are in most respects inferior to using a battery.
It's been years since I saw a bicycle with a dynamo on it for similar reasons.