New devices run on Wi-Fi signals alone

Engineers at University of Washington are working on a new type of tech called "Wi-Fi backscatter" that only needs a signal from a router to power up and communicate.

Michael Franco
Freelancer Michael Franco writes about the serious and silly sides of science and technology for CNET and other pixel and paper pubs. He's kept his fingers on the keyboard while owning a B&B in Amish country, managing an eco-resort in the Caribbean, sweating in Singapore, and rehydrating (with beer, of course) in Prague. E-mail Michael.
Michael Franco
3 min read

Wi-Fi backscatter devices would communicate by altering the signal going from routers to other devices, like your laptop. Video screenshot by Michael Franco/CNET

Wherever you are right now, there's a good chance that streams of energy and data are flying past your head in the form of Wi-Fi signals. Now, researchers at the University of Washington have discovered a way to harness the energy in those waves to not only power small devices, but also connect those devices to the signal and thereby, the Internet.

"Called Wi-Fi backscatter, this technology is the first that can connect battery-free devices to Wi-Fi infrastructure," says a UW news story about the discovery.

The researchers believe their invention could be a major step forward in the development of the Internet of Things, the world in which all of our devices -- even appliances like refrigerators and coffee makers -- connect to each other and to the Internet.

"If Internet of Things devices are going to take off, we must provide connectivity to the potentially billions of battery-free devices that will be embedded in everyday objects," said Shyam Gollakota, a UW assistant professor of computer science and engineering involved in the work. "We now have the ability to enable Wi-Fi connectivity for devices while consuming orders of magnitude less power than what Wi-Fi typically requires."

To find out exactly how the Wi-Fi backscatter devices work, Crave contacted Bryce Kellogg, a doctoral student in electrical engineering and co-author on the research, which will be published at the Association for Computing Machinery's Special Interest Group on Data Communication's annual conference this month in Chicago. He explained that the gadgets function by either reflecting or not reflecting the Wi-Fi signal running between say, a router and a laptop. That interruption in the signal can be then be read by software on the laptop much in the same way binary code is interpreted.

He says that the devices alter the Wi-Fi signal by modulating their radar cross-section. "You can think of radar cross-section as the 'size' of the object as seen by radio waves," he said. "For example, a stealth bomber has a small radar cross-section so it appears 'small' to radio waves. This means it doesn't reflect very well and can't be seen on radar. We can change the radar cross-section of an antenna electrically, without changing the size of the antenna."

So that's how the devices interact with the Wi-Fi signal, but what then?

"Once we are able to reflect [or not] reflect Wi-Fi signals, you can think of the functionality like a signal mirror," Kellogg told me. "I can send you messages in binary by reflecting the sun at you (1) or not (0). Wi-Fi backscatter works in a similar way."

The technology would theoretically allow you to have sensors or other small devices all over your home (or your body) that would never need their batteries changed, would always be on (as long as your router was working), and would all be able to communicate with each other. Certainly sounds like a big step toward the Internet of Things to me.

In addition to publishing their results, the team of engineers also plans on starting a company to develop and promote the Wi-Fi backscatter technology.