Imagine the days when you would not have to worry about your phone running out of battery.These days are not that far.The scientists at the University of Washington have created the first working battery-free cellphone prototype.
The conventional cellular transmission is carried out by converting analogue signals picked by cellphone to digital signals that are relayed across the mobile network.The conversion is what makes voice calls possible between handset and base station but this conversion takes about 800 milliwatts of power for making a call.
It would not be possible to harvest this much power from ambient radio signals. In order to overcome this limitation, scientists figured out a way to lower the need for power.The battery-free cellphone keeps everything analogue.It takes advantage of tiny vibrations in a phone’s microphone or speaker that occur when a person talks on the phone.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 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.
The battery-free phone will still require a power of about 3.5 milliwatts. To harvest this power, the team has used two modes.The prototype can operate on power obtained from ambient radio signals transmitted by base station up to 31 feet away. While harvesting power from ambient light, the phone was able to communicate with a base station 50 feet away using a tiny solar cell. The team has also made Skype calls using its battery-free phone, demonstrating that the prototype made of commercial, off-the-shelf components can receive and transmit speech and communicate with a base station.
They have designed a custom base station to transmit and receive the radio signals. But that technology conceivably could be integrated into standard cellular network infrastructure or Wi-Fi routers now commonly used to make calls as published in their News. Now the research team is planning to improve device’s range and encrypting conversation to make them secure.