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A fully autonomous ultra-low power hybrid RF/photovoltaic energy harvesting system with −25 dBm sensitivity

This study discusses the design process of a novel fully autonomous ultra-low power hybrid RF/photovoltaic energy harvesting system. As a result of the simulated and measured relationship between the output voltage of the rectifier and the load resistance value, the optimal rectifier topology and the charge tank capacitor value are analytically determined. One proof-of-concept designed and fabricated rectifier prototype exhibits the peak and average RF-dc conversion efficiency of 24.0% and 17.6% while charging a charge tank capacitor with −20 dBm of RF power. Similarly, a photovoltaic powered dc-dc converter circuit which requires the minimum power of 59 nW and operates under the low light irradiation of 3 lx (440 nW/cm2) is designed and features the capability of successfully charging the output capacitor up to more than 2.4 V with the output power of 643 nW from −20 dBm of RF input power. The proposed system can generate net positive output power from −25.0 dBm of RF input power.