MagMIMO senses where your phone is and fires a targeted magnetic field to keep it charged up – so you'll never have to plug in again

Ditch the pesky cable (Image: Nono Kalvo/Keystone USA-Zuma/Rex)

PREPARE to cut the cord. Charging your phone may soon be as simple as sitting down at your desk, thanks to a device called MagMIMO that can charge phones at a distance.

Wireless chargers already exist, but they require a phone to be right next to a charging pad. “With charging pads you have to remember to take your phone out of your pocket and place it on the pad, positioned in exactly the right way,” says Dina Katabi of the Massachusetts Institute of Technology, who is leading the team building MagMIMO.

“In our vision we wanted to have people’s phone charge the minute they are sitting next to their desk: they go to a meeting, they come back, the phone starts charging again,” she says.


At a distance of 30 centimetres, Katabi’s prototype can charge an iPhone 4s battery from dead to full in just under 5 hours. It doesn’t matter what orientation the phone is in – upside down in a pocket or flat on the desk – and the phone needn’t be stationary. Katabi is now working to boost the range.

The prototype can wirelessly charge the phone in your pocket from 30 centimetres away

MagMIMO borrows a trick from radio communications: advanced Wi-Fi routers can detect when a computer is connecting to them and boost the signal in their direction. MagMIMO does the same thing, but using magnetic fields instead of radio waves. An array of wire coils generates a magnetic field and when a phone disrupts that field, MagMIMO senses it and focuses on the phone by creating a slightly different field with each coil. The magnetic fields reinforce each other so as to maximise the strength of the overall field reaching the phone.

In testing the prototype, Katabi and her colleague Jouya Jadidian connected a small wire coil to the iPhone’s charging port. The magnetic field induces a current in this coil, charging the phone. Several models of phone already come with such a coil built in, and more will soon be on the market.

As well as eliminating “battery anxiety” for smartphone owners, robust wireless charging is crucial for making wearable technology like smart watches and headsets more appealing to consumers. These smaller devices have less room for batteries, says technology analyst Ross Rubin at Reticle Research in New York City, and our power outlets are already crowded with wires for topping up mobile devices.

“MagMIMO consumes as much power as existing solutions, yet it can charge a phone remotely without being removed from the user’s pocket,” the team wrote in a paper presented last week at the International Conference on Mobile Computing and Networking in Maui, Hawaii. They note that, unlike strongly focused Wi-Fi, focused magnetic fields do not have a heating effect on human tissue.

“The dream is that we’d never have to worry about charging our gadgets again,” Rubin says. “Wireless power would be like Wi-Fi, in just about every home and many public places too.”

This article appeared in print under the headline “Wireless charge from afar”