Soljačić started searching for ways to transmit power wirelessly. Instead of pursuing a long-distance scheme like Tesla's, he decided to look for midrange power transmission methods that could charge--or even power--portabl­e devices such as cell phones, PDAs, and laptops. He considered using radio waves, which effectively send information through the air, but found that most of their energy would be lost in space. More-targeted methods like lasers require a clear line of sight--and could have harmful effects on anything in their way. So Soljačić sought a method that was both efficient--able to directly power receivers without dissipating energy to the surrounding­s--and safe. He eventually landed on the phenome­non of resonant coupling, in which two objects tuned to the same frequency exchange energy strongly but interact only weakly with other objects. - Alan Levine