First Battery-Free Cellphone that Operates by Harvesting Ambient Energy

A group of researchers from the University of Washington has invented the battery-free cell phone that is believed to be a major step in moving beyond chargers and cords. The phone requires just a few microwatts of power to operate which is harvested either from ambient radio signals or ambient light. 

 

The team demonstrated the working of the phone by making audio as well as Skype calls. It showed how the prototype made of commercial, off-the-shelf components could receive and transmit speech and communication with a base station. The details of this technology have already been published in a paper on July 1. 

 

This team including computers scientists and electrical engineers succeeded in eliminating a power-hungry step in the most modern cellular transmissions i.e. converting analog signals into digital data such that it can be understood by the phone. The conversion takes so much of energy that it’s almost impossible to design a phone that can rely on ambient power sources.

 

In order to counter this issue, the battery-free cell phone makes use of tiny vibrations in a phone’s microphone or speaker while the user is talking on a phone or listening to the caller on the other side.

 

There’s an antenna that converts this motion into changes in standard analog radio signal emitted by a cellular base station. This step encodes speech patterns in reflected radio signals in a way that uses a negligible amount of power. 

 

 

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

 

The prototype has been built by using off-the-shelf components on a PCB and it can perform a lot of functions like:

 

• Transmitting speech and data 

• Receiving user input via buttons

• Receive incoming calls on Skype

• Dial out and put callers on hold

 

Talking about the power requirements of the battery-free phone, the prototype needs 3.5 microwatts. The team demonstrated to harvest this energy from 2 different sources:

 

 Ambient radio signals transmitted by a base station up to 31 feet away

 Ambient light with a tiny solar cell to communicate with a base station located 50 feet away

 

The research team is planning to improve the battery-free phone’s operating range and encrypting conversations to make them secure. They are also working on streaming video over a battery-free cell phone and add a visual display feature to the phone in the form of low-power E-ink screens.