Researchers develop battery-free cell phone that uses almost no power

A prototype battery-free cell phone harvests what little energy it needs from radio signals and light.

Wireless technology now allows electric vehicles to charge as they travel and smartphones to recharge using their screens as solar panels. Now, researchers at the University of Washington have eliminated not just the phone charger and cord, but the entire battery. The team has developed the first battery-free cell phone, using only a few micro-watts of power, which it harvests from either ambient radio signals or light.

The prototype phone reduces the amount of electricity needed to operate to a bare minimum by eliminating the step that takes up the most energy – converting analog signals into digital data. Instead, the new phone uses tiny vibrations in the phone’s speaker, which occur when a person talks or listens, into encoded signals that can be transmitted by a base station. Once the amount of power required was reduced to a miniscule 3.5 microwatts, the team was then able to harvest this power from ambient radio signals, also transmitted by the base station; and from ambient light, using a solar cell the size of a grain of rice. Using the phone, researchers were able to make a Skype call as proof-of-concept.

The prototype phone was constructed using off-the-shelf components on a printed circuit board. Although the phone requires a custom base station to operate, the technology could conceivably be integrated into cell towers and wi-fi routers, theoretically providing continuous battery-free cell phone coverage. The team plans to focus next on improving the phone’s operating range and developing encryption for security, as well as developing a way to stream videos and add a visual display that uses low-power e-ink screens. What effect might battery-free cell phones have on the way we communicate?