The first battery-free cellphone
RingPlus News Service Los Angeles July 14th, 2017:
A small group computer scientists and electrical engineers at the University of Washington have created the first battery-free phone that harvests power from ambient radio signals or light. The device is described in a paper published in the, “Proceedings of the Association for Computing Machinery on Interactive, Mobile, Wearable and Ubiquitous Technologies.” The device itself consumes almost zero power according to Dr. Shyam Gollakota. To achieve the extremely low power consumption, the team had to rethink how cellphones are designed. The converting of analog signals which convey sound into digital data that a phone can understand takes so much energy to complete that up until now, has been the reason why it had proved impossible to create a device which can be powered by ambient power sources.
The battery-free cellphone takes advantage of tiny vibrations that come from the microphone and speaker when making a call. An antenna connected to the mic and speaker converts the vibrations into changes in standard analog radio signal emitted by a cellular base station. To transmit speech, vibrations from the microphone are used to encode speech patterns in the reflected signals. To receive speech, the device converts encoded radio signals into sound vibrations which are received through the speaker. In the prototype, you must switch between transmitting and receiving speech by pressing a button. The device essentially encodes speech patterns in reflected radio signals in such a way that uses almost no power.
The prototype still requires some energy, specifically around 3.5 microwatts. They harvest the necessary energy from two different sources, one being through harvesting RF signals from a basestation 31 ft. away and the other using ambient light harvested from tiny photodiodes on the device. When using light from the tiny photodiodes, the team demonstrated that the device could communicate with a basestation which was 50 ft. away.
All the calls were completed using Skype, the team was able to dial out, receive a call, and even place a call on hold with their device. Dr. Vamsi Talla, first author, believes that their basestation could be integrated into every Wifi router and cellular network infrastructure. This could mean a battery-free device with the capability to be used pretty much everywhere. The team will continue to develop their device with improving the devices range and call encryption to make calls secure.