Researchers have invented a "battery-free " cellphone, which harvests all the power it needs to function from ambient radio signals and light, according to the University of Washington (UW). The prototype phone is capable of making voice calls using current off-the-shelf components.

Publishing in the Proceedings of the Association for Computing Machinery on Interactive, Mobile, Wearable and Ubiquitous Technologies, the UW team announced that they eliminated a power-hungry step in cellular transmissions, namely converting analog signals that convey sound into digital data that a phone can understand, which consumes so much energy that it's been impossible to design a phone that can rely on ambient power sources.

Instead, the new technology 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 analog radio signal emitted by a cellular base station. The process essentially encodes speech patterns in reflected radio signals in a way that uses almost no power.

According to the UW team, the prototype phone can successfully perform basic phone functions, transmitting speech and data and receiving user input via buttons.

"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 UW. 

"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."

However, the phone does require a small amount of energy to perform some other operations. The prototype has a power budget of 3.5 microwatts.

Next, the research team plans to focus on improving the battery-free phone's operating range and making it secure.

(Source: Xinhua)