Unwired energy

Powering your laptop computer or cell phone might one day be done the same convenient way many people now surf the Web—wirelessly. The idea of wireless energy transfer is not new. Nikola Tesla worked on long-range energy transfer more than a century ago but failed to develop a practical method. And coils within power transformers inductively transfer electric currents to each other without touching. At November’s Industrial Physics Forum of the American Institute of Physics, held in San Francisco, Marin Soljačić described a new scheme he developed at MIT with Aristeidis Karalis and John Joannopoulos to transfer energy using electromagnetic resonances (see figure). One way to implement the scheme is via conducting wire rings interrupted by capacitors. An energy-transmitting ring would fill the space around itself with a nonradiative, evanescent electromagnetic field. Energy would only be picked up by appliances with special antennas designed to resonate with the field:...