Researchers develop battery-free cell phone prototype

July 06, 2017 // By Rich Pell
Researchers at the University of Washington (Seattle, WA) have developed a cellphone prototype that is powered only by the energy it harvests from its surrounding environment.

The phone is based on "ambient backscatter," which, according to the researchers, "transforms existing wireless signals into both a source of power and a communication medium." Initially used to develop a backscatter communications-based system called " Passive Wi-Fi " designed to dramatically reduce the power of Wi-Fi transmissions, the concept is being applied to converting specific RF signals into power.

According to a Wired interview with the researchers, they needed to go beyond Passive Wi-Fi to achieve voice calls on their battery-free phone. Given the power requirements of converting human speech to digital, the phone instead uses an all-analog backscatter process.

"If you can communicate using analog technology, you're actually more power efficient," says Vamsi Talla, a research associate at the University of Washington's Sensor Systems Laboratory, led by Joshua Smith, which earlier this year spun out Jeeva Wireless , a company designed to commercialize a passive Wi-Fi system based on backscatter technology.

To save power, the phone uses some external circuitry, which converts and connects to the digital cellular network, located in a nearby prototype basestation. The basestation signals - low-power transmissions on an unlicensed frequency - are used by the phone for its energy harvesting.

That circuitry could be built into commercial Wi-Fi routers or phone towers, say the researchers. If installed in the latter, they say, the system's range could be increased from about 15 feet to "perhaps a kilometer."

Currently the phone prototype has no display and only a touch-sensitive number pad. A standard large touchscreen would increase the phone's power requirements by over one hundred thousand times.

The researchers plan to add an e-ink display and improved call quality to their next-generation device. Pricewise, using off-the-shelf components, the current prototype is said to be "cheaper than a normal phone," and would be even less expensive if mass produced.

For more, see " Passive Wi-Fi: Bringing Low Power to Wi-Fi Transmissions ." (PDF)