Scientists present battery-free phone that works on light and RF

Scientists at the University of Washington have presented their research on a phone that doesn’t use a battery. The prototype device uses 3.5 microwatts of power, which comes from ambient light and RF signal from a base station.

The university pays attention to the recently published paper in a press release. It states that the low energy consumption of the device is due to not digitizing analog signals. Modern telephones do this, which, according to the researchers, consumes a lot of energy. Instead, the captured vibrations are transmitted directly by voice in the form of an analog signal.

It uses backscatter, which means reflecting signals. Only digital signals are used when establishing a connection to the base station, the researchers explain. In this way they are able to have a conversation via Skype, as they demonstrate in an accompanying video. It can be heard that the sound quality is not the same that modern telephones provide, but that speech is intelligible. The device must be manually set for ‘transmit’ or ‘receive’.

An earlier message from Wired shows that the base station is needed to connect to the mobile network. A low frequency is used, which in the US falls outside the regulated frequency space. The phone cannot be more than 15 meters from the base station. According to the researchers, this station can be built into mobile network equipment or into Wi-Fi routers in the future.

The phone gets the necessary energy by collecting ambient light with a small solar cell. In addition, the rf signals from the base station are converted into energy by means of an antenna. It is not clear whether the device can also convert other signals. In the future, the scientists want to improve the range of the device and encrypt conversations. Video streaming and adding a screen based on e-ink are also planned.