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This Cellphone Doesn't Need a Battery to Run

by Katie Moritz
September 12, 2017 | Our Future

For some folks, their cellphone's battery falling below 10 percent is cause for panic. But what if cellphones of the future don't require any charging? In fact, what if they hardly use any energy at all?

Scientists at the University of Washington have developed a cellphone that uses almost zero energy to make and receive calls. The energy it does use (just a few microwatts) is captured from ambient light and radio waves. That means no battery and no charging necessary. All the phone needs to run itself it can take from its own environment, using a solar cell the size of a grain of rice.

To say it's a minimalist design is an understatement—the invention only makes calls, something less and less people use their smartphones for regularly. But the technology—which the researchers say is the world's first battery-free cellphone—could be a jumping-off point for more complex models to come. Work has begun on giving the phone a low-power display and the ability to stream video.

“We’ve built what we believe is the first functioning cell phone that consumes almost zero power,” said Shyam Gollakota, an associate professor of computer science and engineering at the University of Washington and coauthor of the research behind the phone, in a news release about the technology.

“To achieve the really, really low power consumption that you need to run a phone by harvesting energy from the environment, we had to fundamentally rethink how these devices are designed.”

A Wifi phone that never dies

The phone, made from commercially available materials and a 3-D printed circuit board, makes its calls via Skype, which means it does need a Wi-Fi signal in order to work.

But eliminating the need to convert speech into digital data to transmit it to the person on the other end of the call allows the tiny phone to operate on almost nothing. The power that's needed to convert sound to digital data has made it impossible to create a phone that runs on ambient energy, until now.

Cellphone pbs rewire

Instead of converting sound to digital information, the device converts movement of a little antenna near the phone's microphone into deviations in a standard analog radio signal emitted by a cellular base station. The team built their own base station for this purpose, but the researchers believe this technology could be integrated into cell towers or Wi-Fi routers.

“You could imagine in the future that all cell towers or Wi-Fi routers could come with our base station technology embedded in it,” researcher Vamsi Talla said. “And if every house has a Wi-Fi router in it, you could get battery-free cell phone coverage everywhere.”

When you talk, the little antenna vibrates. Those vibrations are translated into words on the other end of the call. And doing that requires almost zero energy.

Using these low-energy workarounds, the prototype can dial out, receive incoming calls and place callers on hold.

A battery-free future?

You can't yet order up an Uber on the tiny device, but the battery-free technology might be the jumping-off point for more complex—and more versatile—technology to come, researchers think.

“The cellphone is the device we depend on most today," UW electrical engineering professor Joshua Smith said. "So if there were one device you’d want to be able to use without batteries, it is the cellphone. The proof of concept we’ve developed is exciting today, and we think it could impact everyday devices in the future.”

Katie Moritz
Katie Moritz was Rewire's senior editor from 2016-2020. She is a Pisces who enjoys thrift stores and pho. Follow her on Twitter @katecmoritz.
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