University of Washington researchers present a world first-- a mobile phone that needs no battery to make calls, since it uses so little power it runs on a "few microwatts" harvested from ambient radio signals or light.
In fact, the phone needs just 3.5 microwatts for continuous operation, and makes both regular and Skype calls. The prototype shown by the researchers is built using off-the-shelf components, receives and transmits speech, and communicates with a base station. To achieve such power savings, the team eliminated the need to convert the analog signals making sound into digital data. Instead, the battery-free phone uses the vibrations in a microphone or speaker caused when the user speaks into a phone or listens to a call.
Even the antenna uses no almost no power, since it converts vibrations into changes in standard analog radio signals emitted by a cellular base station, encoding speech patterns into reflected radio signals. To transmit speech, the phone uses vibrations from the microphone to encode speech patterns in the reflected signals. To receive speech, it converts encoded radio signals into sound vibrations picked up by the speaker.