An integrated thermal and RF energy harvesting system with rectifying combination and storage controller for IoT devices

This work presents an integrated thermal/RF energy harvester. The harvesting system can combine energy from two sources simultaneously (one DC and one AC) and deliver a regulated combined voltage of 1.75 V to a load and a storage controller. The output power of the harvester is in the range of hundreds of μWatts which is suitable for low-power wireless sensor networks. Maximum power point tracking (MPPT) is achieved by reconfiguring the number of stages of the DC path, the frequency driving the charge pump, and the capacitors of the matching network in the RF-path. The storage controller charges a supercapacitor to 3.5 V to power up the system during power shortage periods. The system is implemented in a 180 nm CMOS technology and utilizes a total on-chip capacitance of 2.4 nF. The peak end-to-end efficiency of the system reaches 60.3 % at output load power of 1.275 mW.