Ultra-low power autonomous 2.4GHz RF energy harvesting and storage system

We present an autonomous end-to-end 2.4GHz RF energy harvesting and storage system suitable for harvesting energy from WiFi and similar devices. The system is designed to collect ultra-low power ambient RF input energy and automatically store it into a battery. Previous work in this area required a pushbutton switch for full functionality - RF energy is first stored in a capacitor and manually transferred into a battery. In this work, in addition to the main harvester, an auxiliary control system is developed to replace the pushbutton and achieve fully autonomous energy harvesting and storage. Two design approaches are proposed for the control system. The tradeoffs of each technique will be discussed. The designed control systems were integrated into the main harvesting structure. Experimental results indicate that the system autonomously stores 241μJ into a NiMH battery after 30 minutes with an incident power (at the feedpoint of the antenna) of -21dBm.