World’s First Battery-Free Cell Phone Uses Only Ambient Power

And it’s actually surprisingly small!

Credit: University of Washington

Imagine a world where you never have to worry about your cell phone battery dying. This may soon become a reality, as researchers at the University of Washington have invented a battery-free cell phone that works with the power of ambient light and radio waves. The research was published July 1st in the journal Proceedings of the ACM, titled “Battery-Free Cellphone.

“We’ve built what we believe is the first functioning cell phone that consumes almost zero power. 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,” explained Shyam Gollakota, co-author of the research.

Collaborating researcher Bryce Kellogg demonstrates the phone’s use in a video. Dialing the phone number with capacitive touch buttons, the phone transfers digital packets to a custom base station— which can currently be up to 50 feet away. The base station dials the number using Skype. The user can hear over headphones and pushes a button on the phone in order to speak into the built-in microphone.

They explain the audio is transferred using the zero-power analog backscatter. According to a university press release, “An antenna connected to those components converts that motion into changes in standard analog radio signal emitted by a cellular base station. This process essentially encodes speech patterns in reflected radio signals in a way that uses almost no power.”

Credit: University of Washington

According to the study, the device can sense speech and connect to the headphones, switching between uplink and downlink communications in real time. The system does this by optimizing transmission and speech reception while simultaneously harvesting power, which allows the cell phone to work continuously.

The prototype was built simply using “commercial-off-the-shelf components on a printed circuit board.” Developers of the technology hope to continue making improvements, particularly by extending the range of the base station transmission, encrypting conversations and adding a visual screen.

“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 lead researcher Joshua Smith. “The proof of concept we’ve developed is exciting today, and we think it could impact everyday devices in the future.”

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