7 September 2011—As smartphones and other portable gadgets push the limits of handheld computing, their hunger for electricity has only increased—with no end in sight. A new technology aims to address this issue, not by seeking bigger and better batteries but by looking instead to the shoes on our feet.
When we walk, our bodies create up to 40 watts of mechanical power as heat when our feet strike the ground. A special electricity-generating cushion placed inside the soles of a regular pair of shoes can transform some of that footfall power into several watts of electricity. Over the course of a single day, the generated energy, which gets stored in a small battery in the sole, provides enough electricity for a pedestrian to extend her smartphone’s battery life, for a soldier to augment his portable power needs in the field, or for someone in a developing nation without an electrical grid to power a night’s worth of LED home light use.
The idea of harvesting body energy for portable electronics is certainly not new, although some of this technology is. In 1996, Thad Starner at the MIT Media Lab calculated (PDF) that piezoelectric generators—solids that generate tiny currents when stretched or stressed—could theoretically generate up to 5 W of electricity at a brisk walking pace.
Starner’s forecasts have proved optimistic. Today’s best known piezoelectric footwear—Nike
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