Select your localized edition:

Close ×

More Ways to Connect

Discover one of our 28 local entrepreneurial communities »

Be the first to know as we launch in new countries and markets around the globe.

Interested in bringing MIT Technology Review to your local market?

MIT Technology ReviewMIT Technology Review - logo

 

Unsupported browser: Your browser does not meet modern web standards. See how it scores »

Small, battery-powered gadgets make powerful computing portable. Unfortunately, there’s still a continual need to recharge the batteries of phones, laptops, cameras, and MP3 players by hooking them up to a tangle of wires. Now researchers at MIT have proposed a way to cut the cords by wirelessly supplying power to devices.

“We are very good at transmitting information wirelessly,” says Marin Soljačić, professor of physics at MIT. But, he says, historically, it’s been much more difficult to transmit energy to power devices in the same way. Soljačić, who was a 2006 TR35 winner (see “2006 Young Innovator”), and MIT colleagues Aristeidis Karalis and John Joannopoulos have worked out a theoretical scheme for a wireless-energy transfer that could charge or power devices within a couple of meters of a small power “base station” plugged into an electrical outlet. They presented the approach on Tuesday at the American Institute of Physics’s Industrial Physics Forum, in San Francisco.

The idea of beaming power through the air has been around for nearly two centuries, and it is used to some extent today to power some types of radio-frequency identification (RFID) tags. The phenomenon behind this sort of wireless-energy transfer is called inductive coupling, and it occurs when an electric current passes through wires in, for instance, an RFID reader. When the current flows, it produces a magnetic field around the wires; the magnetic field in turn induces a current in a nearby wire in, for example, an RFID tag. This technique has limited range, however, and because of this, it wouldn’t be well suited for powering a roomful of gadgets.

To create a mid-range wireless-energy solution, the researchers propose an entirely new scheme. In it, a power base station would be plugged into an electrical outlet and emit low-frequency electromagnetic radiation in the range of 4 to 10 megahertz, explains Soljačić. A receiver within a gadget–such as a power-harvesting circuit–can be designed to resonate at the same frequency emitted by the power station. When it comes within a couple of meters of the station, it absorbs the energy. But to a nonresonant device, the radiation is undetectable.

Importantly, the energy that’s accessed by the device is nonradiative–that is, it doesn’t propagate over great distances. This is due to the low frequency of the radio waves, says John Pendry, professor of physics at Imperial College, in London. Electromagnetic radiation comes in two flavors: near-field and far-field. The intensity of low-frequency radiation drops quickly as a person moves farther away from the base station. In other words, the far-field radiation that propagates out in all directions isn’t very strong at low frequencies, hence is essentially useless. (Wi-Fi signals, in comparison, are able to remain strong for tens of meters because they operate at a higher frequency of 2.4 gigahertz.)

41 comments. Share your thoughts »

Tagged: Communications, Energy

Reprints and Permissions | Send feedback to the editor

From the Archives

Close

Introducing MIT Technology Review Insider.

Already a Magazine subscriber?

You're automatically an Insider. It's easy to activate or upgrade your account.

Activate Your Account

Become an Insider

It's the new way to subscribe. Get even more of the tech news, research, and discoveries you crave.

Sign Up

Learn More

Find out why MIT Technology Review Insider is for you and explore your options.

Show Me
×

A Place of Inspiration

Understand the technologies that are changing business and driving the new global economy.

September 23-25, 2014
Register »