Battery-free mobile

10 July 2017

Credit: Mark Stone/University of Washington

Researchers have created a phone which needs no batteries; rather, the device harvests the few microwatts of power it requires from either ambient radio signals or light.

The team even made 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 cellphone that consumes almost zero power,” said co-author Shyam Gollakota, an associate professor in 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 team of computer scientists and electrical engineers eliminated a power-hungry step in most modern cellular transmissions, and effectively converted analogue signals that convey sound into digital data that a phone can understand. This process consumes so much energy that it has been impossible to design a phone that can rely on ambient power sources.

Instead, the battery-free cellphone 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.

An antenna connected to those components converts that motion into changes in standard analogue 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: Mark Stone/University of Washington

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 that are picked up by the phone’s speaker. In the prototype device, the user presses a button to switch between these two ‘transmitting’ and ‘listening’ modes.

Using off-the-shelf components on a printed circuit board, the team demonstrated that the prototype can perform basic phone functions – transmitting speech and data and receiving user input via buttons. Using Skype, researchers were able to receive incoming calls, dial out and place callers on hold with the battery-free phone.

“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 faculty lead Joshua Smith, professor in both the Allen School and UW’s Department of Electrical Engineering. “The proof of concept we’ve developed is exciting today, and we think it could impact everyday devices in the future.”

Credit: the University of Washington, washington.edu


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