“My phone’s dead” may soon be a phrase of the past as the ability to shed your cell’s cords, portable chargers, and even batteries is quickly becoming a possibility.
The University of Washington recently unveiled a study touting new uses for old technology that will allow users to make calls on battery-free phones. The phone is outlined in a paper that was published at the beginning of this month in the Proceedings of the Association for Computing Machinery on Interactive, Mobile, Wearable and Ubiquitous Technologies.
The prototype battery-free phone harvests the small amounts of power it needs (3.5 microwatts to be exact) through radio signals or ambient light. Typically the most power-hungry operation a phone goes through is converting analog signals that convey sound into digital data that a phone can understand. This had to be bypassed in order to create a battery-free device.
Instead, this new prototype can use the tiny vibrations on a microphone created by a person’s voice and convert that motion into changes in standard analog radio signals emitted by a cellular base station. In this case, the prototype’s base station is the popular app Skype. This choice is a deliberate one according to the study’s lead author Vamsi Talla.
“Normally, phones use base stations like their own telecom providers to connect calls,” says Talla. “We chose Skype because it was the easiest to integrate with our system.”
The prototype does have a range in terms of how it gathers power. Radio signals have to be 31 feet away or closer for the phone to take in power, or 50 feet with a tiny solar cell the size of a grain of rice.
“The 50-foot limitation is due to our unlicensed spectrum, meaning we don’t pay money to transmit the signal,” says Talla. “Based on our estimates though, we could transmit up to a kilometer, which is exciting because if you look at where cellular tech is progressing, it’s going to 5G with smaller and more plentiful cell towers.”
Two immediate practical uses come to mind. In cities, the battery-free prototype could allow emergency calls to be made on phones with very little or no charge left. Alternatively, it could be used in developing countries where infrastructure to charge a phone may not be readily available. In this case, battery-free phones could last years or even decades, as the battery is often the first thing to fail in current phones.
The current prototype is very basic but it has the capability to change the way we view portable power sources. Along with increasing the transmission range, the next areas of focus for the University of Washington group include low-power display screens and video streaming.