Wireless power transfer is old news—more than a century ago, Nikola Tesla built magnetic coils that transmitted power without cables. But Tesla’s coils also tended to expel bursts of superhot plasma. This past June, MIT researchers announced their own coil-based breakthrough in wireless electricity—called WiTricity—that’s mercifully plasma-free.

WiTricity exploits a phenomenon known as magnetically coupled resonance, which allows two objects resonating at the same frequency to exchange energy efficiently. The team was able to wirelessly power a 60-watt light bulb using a pair of 20-in.-dia. copper coils. Drawing power from an electrical outlet, the source coil created a magnetic field, which was 7 ft. in diameter, transmitting at a frequency of 10 MHz. (Many cellphones, by com-parison, operate at 2 GHz.) Seven feet away, a receiving coil was also resonating at 10 MHz, pulling enough energy from the field to power an attached light bulb.

Because it transmits at such a low frequency, WiTricity’s magnetic field passes through intervening objects, and doesn’t appear to pose a threat to people or pets. Within five years, the team hopes to release a commercial product with better power efficiency, a larger field and more compact coils, capable of running or charging multiple devices.