Ba ery Free Cellphone

1 INTRODUCTION is paper asks the following question: Can we design a ba ery-free cell phone that operates while consuming only a few micro-wa s of power? Given that ba eries add weight, bulk, cost, require recharging and replacement, a positive answer would enable phones that have two-way communication capabilities without the need for ba eries. Further, a microwa-power phone can use cheap and lightweight harvesting sources including radio signals and photodiodes instead of bulky and expensive solar cells. Finally, such a design would represent a fundamental leap in the capability of ba ery-free devices. e key challenge in achieving this is that a cellphone is required to perform multiple basic operations: sensing speech at the device, transmi ing it to the base station, receiving speech information from the base station and nally actuating the speaker/earphones. Designing a ba ery-free cell phone system requires us to perform all these functions, in real time, using only a few micro-wa s of power. To appreciate this challenge, it is instructive to look at existing low-power ba ery-free sensor prototypes. RF-powered sensors such as accelerometers [35], humidity [34] and temperature sensors [35] are heavily dutycycled to send sensor data once every few seconds or minutes. RF-powered cameras [27, 37] require extensive