More 60-Second Science
June 11, 2007 Recharging Batteries Wirelessly
Cell phones are great, except for one problem: if you forget to recharge the battery, you might get caught without a working phone. But hey, if that phone signal can follow you all over the place, why can’t someone simply beam some electricity at your phone too? Well, researchers at MIT have taken a step toward making that a reality. They call it Wi-tricity (for wireless electricity), and they were able to use it to switch on a 60 watt light bulb from a power source seven feet away - without any wires.
They did the trick by using coupled resonance, which works because two objects of the same resonant frequency exchange energy efficiently. Think of the opera singer who can make a wine glass explode. The MIT system relies on magnetic fields. A copper coil attached to a power source fills the space around it with a magnetic field that oscillates at a particular frequency. Objects within the field convert the magnetism back to electricity. So someday you might leave the house with a spent cellphone and watch it charge up as you walk down the street.