Battery-free Phone Harvests Energy From Ambient Radio Signals

Researchers from the University of Washington developed a phone that requires no batteries. At the moment it is in the prototype phase, the basic phone harvests the minimal power from ambient radio signals, to communicate with a base station making voice calls. According to team, a new phone consumes almost zero energy, built on a printed circuit board it’s capable of very basic functions – send, receive, make and accept calls, and place callers on hold.

When a person talks or listens on a phone, tiny vibrations occur in the microphone, which for the prototype also acts like an earphone. It doesn’t transmit its own radio signals, it piggybacks on the back of the radio signal emitted from a bespoke cellular base station. To transmit speech, an antenna connected to the microphone encodes the user’s speech patterns in the radio signal reflected from the antenna. To  receive a speech involves an antenna converting speech patterns encoded in the radio signals into sound vibrations that are relayed to the phone’s speaker. A user must press a button to switch between listening and transmitting modes. The system still needs about 3.5 microwatts to function, and it harvests this energy from the ambient radio signals of the base station at a distance of up to 9 meters. Using a solar cell about the size of a grain of rice to gather ambient light increases the range 15 meters.

The team is also working on how to encrypt messages and stream videos, and adding a low-power E-ink screen for a display. The video below shows the battery-free phone in action.

Source: University of Washington

The research was published in the Proceedings of the Association for Computing Machinery on Interactive, Mobile, Wearable and Ubiquitous Technologies.


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