Festival-goers struggling to keep their mobile in use over a full weekend will be interested to hear about a battery-free phone developed by researchers at the University of Washington.

The device uses solar power and radio signals, and has already been successful in carrying out tasks such as making calls over Skype.

The phone consists of simple components on a basic circuit board, with the prototype able to operate on just a few microwatts of power instead of relying on the cell batteries used in current mobile phones.

University of Washington

Touch buttons are used to dial a number and make a Skype call. The person’s voice audio is then transmitted through earphones. The person on the other end needs to press down a button while the dialler speaks into an inbuilt microphone. This is also to show that they are listening to the person on the other end.

Vibrations picked up from the device’s microphone are then converted by the phone’s antenna to encode speech patterns in the reflected signals to transmit the speech, and convert encoded radio signals into sound vibrations for the phone’s speaker in order to receive it.

A tiny solar cell the size of a grain of rice in the prototype phone is used to collect ambient light and communicate with another nearby base station. Due to this reliance on being near a base station, the phone’s capabilities out and about are currently limited. However, the project could help push towards the development of phones that require little or no charging.

“You could imagine in the future that all cell towers or Wi-Fi routers could come with our base station technology embedded in it,” co-author Vamsi Talla told the university. “If every house has a Wi-Fi router in it, you could get battery-free cellphone coverage everywhere.”

While the phone is currently incredibly basic with no screen, the researchers have reportedly begun looking into connecting an e-ink display, which also operates on recycled solar power to provide a visual.

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