Battery-free Cellphone Works By Harvesting Power From Ambient Radio Signals

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University of Washington engineers present the first battery-free cellphone design that consumes only a few micro-watts of power. The new design can sense speech, actuate the earphones, and switch between uplink and downlink communications, all in real time.

image credit: washington.edu

The system developed by researchers from the Allen School of Computer Science & Engineering and the UW Department of Electrical Engineering optimizes transmission and reception of speech while simultaneously harvesting power which enables the battery-free cellphone to operate continuously.

image credit: washington.edu

The battery-free cellphone takes advantage of tiny vibrations in a phone’s microphone or speaker that occur when a person is talking into a phone or listening to a call.

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An antenna connected to those components converts that motion into changes in standard analog radio signal emitted by a cellular base station. This process essentially encodes speech patterns in reflected radio signals in a way that uses almost no power.

To transmit speech, the phone uses vibrations from the device’s microphone to encode speech patterns in the reflected signals. To receive speech, it converts encoded radio signals into sound vibrations that that are picked up by the phone’s speaker. In the prototype device, the user presses a button to switch between these two “transmitting” and “listening” modes.