http://www.sciencealert.com/here-s-how-electricity-harvested-from-the-air-could-power-our-smart-home-gadgets "For the first time, we have solved the problem of harvesting usable energy from a small radio frequency signal." http://www.sciencealert.com/here-s-how-electricity-harvested-from-the-air-could-power-our-smart-home-gadgets