The one caveat is that now the battery-free cell phone does require communication with a unique base station, and this does still require a battery.
Washington, July 6, 2017: In a major leap ahead to life beyond chargers, cords and dying phones, researchers, including one of the Indian-origin, have invented the cell phone that works without batteries.
While it's early days and it's unlikely we'll see this kind of battery-free comms incorporated in today's smartphones any time soon - whose screens and other components require far more power to operate - it's a promising direction for future research, especially considering how fundamental basic phone calls are to modern life.
An antenna connected to those components converts that motion into changes in standard analog radio signal emitted by a cellular base station.
Imagine a smartphone that doesn't need a battery because it consumes nearly no power?
When a person talks or listens on a phone, tiny vibrations occur in the microphone or speaker, which for the prototype is a pair of earphones.
The device uses these vibrations to encode the speech on the radio signal.
A special center was designed for the phone to receive and transmit radio signals, and the prototype reportedly requires three and a half microvolt of energy. The battery-less concept was proven through Skype and a custom base station the team made, after they were able to make calls, put someone on hold, and receive calls on the phone.
But unlike this latest phone, these devices required the phone to go into sleep mode between each task making it more trouble than it's worth. "So if there were one device you'd want to be able to use without batteries, it is the cellphone", said Joshua Smith, Professor at University of Washington.
While battery-less, the system still needs about 3.5 microwatts to function.
Researchers demonstrated how to harvest this small amount of energy from two different sources. Calls need a constant connection to the base station, unlike some IoT devices might, so keeping power flow for the call duration was a particular challenge. In tests the researchers found their mobile phone was functional within 31ft of the base station relying only on energy harvesting ambient radio signals. "So real-time phone operations have been really hard to achieve without developing an entirely new approach to transmitting and receiving speech".
The battery-free phone developed at the UW can sense speech, actuate the earphones, and switch between uplink and downlink communications, all in real time. They will also try to add extra features to the battery-free phone, such as a monitor and streaming video.