Researchers from the University of Washington have developed a cellphone that does not require a battery. The prototype device has a power budget of 3.5 microwatts, which is a fraction of the energy used by conventional cellphones in standby mode. The energy is harvested in two different ways. The device can be powered by ambient radio signals transmitted by a base station, or convert light into energy with a tiny solar cell, the size of a grain of rice.
One of the most power hungry components of the cellphone is the conversion of analog sound signals into digital data that can be interpreted by the device. The battery less device sidesteps this requirement by using an antenna connected to the microphone to change ambient radio signals according to the voice input, to transmit signals. To receive signals, the information encoded in the radio signals are converted to vibrations. The process uses almost no power.
The researchers focused on inventing a cellphone that did not require a battery as it is one of the most commonly used devices today. The team used a custom base station to transmit and receive signals, but conventional mobile towers can potentially incorporate the technology used in the custom base station, to transmit power to the cellphones. Professor Joshua Smith says, "The proof of concept we’ve developed is exciting today, and we think it could impact everyday devices in the future."
In the prototype device, users have to use a button to switch between the transmitting and receiving modes. The researchers were able to place a Skype call, keep users on hold, and dial numbers with the phone. Now the team is working on incorporating a low power e-ink screen, adding functionality for transmitting videos, and encrypting the calls made through the device. The prototype device uses off the shelf components available in electronic stores.