Tom Krupenkin's Power Shoes

Tom Krupenkin knows he’s not the first person to try making shoes that generate electricity. In 1998 researchers at the MIT Media Lab rigged a pair of Nikes to broadcast a stride-powered radio signal. Three years later, Trevor Baylis, the inventor of a popular wind-up radio, made a boot-heel insert that charged his cell phone during a 100-mile trek across the Namib Desert in southern Africa. “The idea itself goes a very long time back, arguably to the beginning of the 20th century,” says Krupenkin, an engineering professor at the University of Wisconsin at Madison.

Those earlier efforts were based on a technology called piezoelectrics—tiny crystals that create a current as they compress and expand—and didn’t make enough power to be practical. MIT’s Nikes generated a few thousandths of a watt, and Baylis had to walk for days to charge his cell phone. Krupenkin and his lab partner, J. Ashley Taylor, have discovered a more efficient approach called reverse electrowetting.