This cell phone doesn't need a battery
The battery-free cell phone is powered by ambient radio signals or light.

Researchers at the University of Washington have invented a prototype phone that makes calls using energy from ambient radio waves and sunlight instead of a battery.

University of Washington engineers have designed a battery-free cell phone that can send and receive calls using only a few microwatts of power.

Researchers have developed a cell phone that pulls energy from the world around it, allowing it to operate without any battery at all.

Given the high energy-demand of cell phones, however, the device uses analog rather than digital capabilities to communicate, essentially resurrecting Cold War-era spy technology.

The battery-free cell phone does away with these conversions by making use of an analog radio signal emitted by a custom-designed base station. The incoming message is heard when an antenna in the phone picks up a pattern in the radio signal and the speaker in the phone converts the pattern into sound waves. The outgoing message is sent when vibrations in the phone’s microphone caused by the user’s voice are used by the antenna to modify the radio signal emitted by the base station. The station picks up the changed signal and sends it to the person on the other end of the call.

The battery-free phone still needs a 3.5 microwatt power source even though all of the conversions between digital and analog are handled in the base station. If it needs power, it still needs a battery, right? Wrong. The research team devised two methods for drawing power from the ambient environment. Enough power to run the phone can be drawn from the radio frequency signals emitted by the base station or from a grain-of-rice-sized solar cell on the phone’s circuit board.

The base station is doing all the heavy lifting by handling the digital/analog conversions and sending the radio signals that power the phone. The researchers claim this doesn’t pose a problem for implementing their system because the base station’s technology can be integrated easily into cellular networks and WiFi routers.