Say What? Researchers Develop First Battery-Free Mobile Phone

“Can you hear me now? Good.” These days, it’s uncommon for us to leave our houses without our smartphones. They’ve become an indispensable tool that we use to communicate, conduct business and “veg out” in our downtime. About the only thing worse than venturing out into the world without our smartphone by our side is actually having our smartphones and staring at a “low battery” warning.

However, researchers from the University of Washington are looking to make batteries a thing of the past when it comes to mobile phones. The team has developed a phone that uses “almost zero power” according to associate professor Shyam Gollakota, who co-authored a paper which detailed the breakthrough.

So how exactly does this phone work? Well, the researchers designed the phone to harvest microwatts of power from RF signals transmitted from a base station that is 31 feet away. Additional power is harnessed via ambient light through the use of miniature photodiodes that are about the size of a grain of rice. While in use, the phone consumes about 3.5 microwatts of power and is capable of communicating with a custom base station that is up to 50 feet away to send and receive calls.

Unlike other “battery-free” devices which must employ sleep/wake states in order to generate enough power to complete routine tasks, the very nature of a mobile phone means that there needs to be an uninterrupted supply of power to complete a call.

“That’s been the biggest challenge — the amount of power you can actually gather from ambient radio or light is on the order of 1 or 10 microwatts,” added co-author and electrical engineering doctoral student Bryce Kellogg. “So, real-time phone operations have been really hard to achieve without developing an entirely new approach to transmitting and receiving speech.”

The phone ditches the traditional analog-to-digital converter, which turns your voice into data, in favor of a system that uses the vibrations from a microphone or speaker to perform the same task. An antenna then converts that motion into radio signals in such a way that very little power is consumed. However, reminiscent of a walkie-talkie, you have to press a button to switch between transmissions and listening modes with the phone.

“You could imagine in the future that all cell towers or Wi-Fi routers could come with our base station technology embedded in it,” continued co-author Vamsi Talla, a former UW electrical engineering doctoral student. “And if every house has a Wi-Fi router in it, you could get battery-free cellphone coverage everywhere.”

Of course, it would take more than harvesting energy from microwaves and ambient light to power today’s modern smartphones. Although the prototype smartphone was able to conduct regular phone calls and Skype calls, modern smartphones need a lot more than a 3.5-microwatt power budget for blazing fast processor, copious amounts of RAM and internal storage, and power-hungry displays.