One night in 2002, MIT physicist Marin Soljacˇic´ heard the chirps of his cell phone letting him know that its battery was losing the last of its juice. Annoyed, he began to wonder if there were any physics principles that would allow the phone’s battery to be charged in a more convenient way. Over the next three years, Soljacˇic´, graduate student Aristeidis Karalis, and physics professor John Joannopoulos worked on and off to devise a theoretical scheme for charging gadgets wirelessly.
“We are very good at transmitting information wirelessly,” says Soljacˇic´. But it’s been much more difficult to transmit power in the same way, because the radiation spreads out, and most of it is lost in the environment. Soljacˇic´ and his team propose developing a power “base station” that would plug into a wall, much like a Wi-Fi base station; but it would emit great energy at close range. Theoretically, when devices such as mobile phones or laptops came within range of the power base station, they would pick up its energy.
In the 1890s, before power cables commonly transported electricity over great distances, physicist and electrical engineer Nikola Tesla proposed beaming it through the air. Today, a form of wireless energy transfer called inductive coupling is used to charge electric toothbrushes. Electricity flowing through the wires in a toothbrush’s base station produces a magnetic field; that field induces a current in the wires of a nearby toothbrush handle, charging the toothbrush’s battery. This technique has limited range, however.
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