A Battery Free-Cell Phone That You Might Just Need Today

Bye powerbank.

Radio waves carry energy when surrounded by transmitters. Same is true with providing power for you home, when you hook all your electronic devices in antennas.

Radio wave propagation follows the inverse square law. The strength of the radio signal weakens by the square of the distance from the transmitter. It doesn’t take long before you’re too far from a transmitter to harvest enough electricity to do useful work.

When you make a phone call, it requires your device to have continuous power. “You can’t say hello and wait for a minute for the phone to go to sleep and harvest enough power to keep transmitting,” said paper co-author Bryce Kellogg, a UW electrical engineering doctoral student, in a press release. “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. So real-time phone operations have been really hard to achieve without developing an entirely new approach to transmitting and receiving speech.”

To solve the problem, the team designed a station that transmits RF signals to the battery-free cell phone. With both the base station and the photodiodes, the phone can operate up to 50 feet from the base station.

To make a call, you just need to punch in the phone number you want to call and the circuit board sends this information via radio waves to the base station in a digital packet. The base station takes this data and makes a call on Skype to a cellular network. The station continues to remain in contact with the phone via radio waves, allowing the caller to hear the other side of the conversation. To speak, you just have to hold down a button to activate the microphone.

The basic design means the phone operates on just a few microwatts!