Soon you won’t need to worry about charging your cell phone at all. The University of Washington’s team of electrical engineers and computer scientists created a cellphone that harvests power from ambient radio waves or light.

This is game-changing technology that significantly reduces the cost of communication devices and opens a path for a new level of devices.

Their phone can hear, play audio via headphones, and switch between up/downlink communication.

“We’ve built what we believe is the first functioning cellphone that consumes almost zero power,” said co-author Dr. Shyam Gollakota, from the Paul G. Allen School of Computer Science & Engineering at the University of Washington.

“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.”

The greatest consumer of energy in a cellphone is transforming analog signals to digital data. So instead, a battery-free cellphone receives energy from the tiny vibrations of the microphone and speakers through an antenna touching them and encodes speech patterns in reflected radio signals in a way that uses almost no power.

To transmit speech, the phone uses vibrations from the device’s microphone to encode speech patterns in the reflected signals. To receive speech, it converts encoded radio signals into sound vibrations through the speaker.

Like a walky-talky, one pushes a button to switch between ‘transmitting’ and ‘listening.’

“The cellphone 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 cellphone,” said senior author Professor Joshua Smith, from the Allen School and the Department of Electrical Engineering at the University of Washington. “The proof of concept we’ve developed is exciting today, and we think it could impact everyday devices in the future.”

This battery-free phone still 3.5 microwatts of power.

“The battery-free device prototype was built using commercial-off-the-shelf components on a printed circuit board,” the researchers said. “It can operate on power that is harvested from RF signals transmitted by a base station 31 feet (9.4 m) away.”

“Further, using power harvested from ambient light with tiny photodiodes, we demonstrated that our device can communicate with a base station that is 50 feet (15.2 m) away.”

Their prototype could perform only basic functions yet was able to make calls on Skype. They are working to improve range and encryption.

“We designed a custom base station to transmit and receive the radio signals. But that technology conceivably could be integrated into standard cellular network infrastructure or Wi-Fi routers now commonly used to make calls,” they said. “You could imagine in the future that all cell towers or Wi-Fi routers could come with our base station technology embedded in it,” said first author Dr. Vamsi Talla, also from the Allen School at the University of Washington. “And if every house has a Wi-Fi router in it, you could get battery-free cellphone coverage everywhere.”


  2. Vamsi Talla et al. 2017. Battery-Free Cellphone. Proceedings of the ACM on Interactive, Mobile, Wearable and Ubiquitous Technologies 1 (2): 25; doi: 10.1145/3090090