Living in a constant search of technology improvements, our goal would be to be able to use devices without any electricity or battery: seemed completely impossible, manufacturers constantly creating new products that can last longer on a single battery charge. A engineers’ team from the University of Washington has passed this step. In fact, they just built a cellphone that doesn’t need a battery. Can you believe it?
Aesthetically, it doesn’t have the design of a normal cell phone: only a printed circuit board with the basics to make phone calls, including a microphone, number pad and headphone jack.
The engineers use photodiodes to absorb photons from light sources and generate electricity and an antenna, so this prototype still uses electricity, it harvests power from sources such as radio waves (-the waves induce electricity to flow through the antenna) and sunlight.
NB* While radio waves carry energy and we're surrounded by transmitters generating these waves, this doesn't mean you could power your home by hooking all your electronics to antennas. That's because radio wave propagation follows the inverse-square law — the strength of a radio signal weakens by the square of the distance from the transmitter. It doesn't take long before you're too far from a transmitter to harvest enough electricity to do useful work. (©electronics.howstuffworks)
To make a call, your device needs continuous power. This, for the engineers the biggest challenge, “-the amount of power you can actually gather from ambient radio or light is on the order of 1 or 10 microwatts. So real-time phone operations have been really hard to achieve without developing an entirely new approach to transmitting and receiving speech." Said the UW electrical engineering doctoral student, Bryce Kellogg, in a PR.
The team created a base station that transmits RF signals to the battery-free cellphone to avoid the problem. In fact, with the station and the photodiodes, the phone can operate up to 50 feet, 15 meters from the base station.
To make a call, you just put the phone number you would like to call, the PCB sends the information to the base station in a digital packet via radio waves. The data is taken by the base station and then is made a call on Skype to a cellular network. You speak via the microphone by holding down a button. The contact between the station and the phone is constant, allowing you to hear your interlocutor.