Researchers have created a battery-free phone that is powered by sunlight

Instead of batteries, a new cell phone harvests the few microwatts of power it needs from a different source: ambient radio signals or light.

Researchers were also able to make Skype calls using the battery-free phone, demonstrating that the prototype—made of commercial, off-the-shelf components—can receive and transmit speech and communicate with a base station.

“We’ve built what we believe is the first functioning cell phone that consumes almost zero power,” says Shyam Gollakota, an associate professor of computer science & engineering at the University of Washington and coauthor of the paper in the Proceedings of the Association for Computing Machinery on Interactive, Mobile, Wearable and Ubiquitous Technologies.


Researchers eliminated a power-hungry step in most modern cellular transmissions—converting analog signals that convey sound into digital data that a phone can understand. This process consumes so much energy that it’s been impossible to design a phone that can rely on ambient power sources.

Instead, the battery-free cell phone takes advantage of tiny vibrations in a phone’s microphone or speaker that occur when a person is talking into a phone or listening to a call.




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


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





“You can’t say hello and wait for a minute for the phone to go to sleep and harvest enough power to keep transmitting,” says coauthor Bryce Kellogg, an electrical engineering doctoral student. “That’s been the biggest challenge—the amount of power you can actually gather from ambient radio or light is on the order of 1 or 10 microwatts. So real-time phone operations have been really hard to achieve without developing an entirely new approach to transmitting and receiving speech.”

The team next plans to focus on improving the battery-free phone’s operating range and encrypting conversations to make them secure. The team is also working to stream video over a battery-free cell phone and add a visual display feature to the phone using low-power E-ink screens.

The National Science Foundation and Google Faculty Research Awards funded the work.



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