University of Washington students’ battery-free cellphone design

Students at the University of Washington have presented what they claim to be the first battery-free cellphone design that consumes only a few micro-watts of power.

Their design can sense speech, actuate the earphones, and switch between uplink and downlink communications, all in real time. The current setup requires the cellphone to be used in a similar manner to a typical push-to-talk device, being unable to work in full duplex mode and requiring the user to push and hold a button when speaking into its microphone.

The system optimises transmission and reception of speech while simultaneously harvesting power, enabling the battery-free cellphone to operate continuously. The battery-free device prototype is built using commercial-off-the-shelf components on a printed circuit board It can operate on power that is harvested from RF signals transmitted by a base station 9.4 metres away.

Using power harvested from ambient light with tiny photodiodes, the students have shown that their device can communicate with a base station 15.2 metres away.

They have also performed a Skype call using the battery-free phone over a cellular network, via their custom bridged base station, which they believe is a major leap in the capability of battery-free devices and a step towards a fully functional battery-free cellphone.