Cooperative Integration of Harvesting RF Sections for Passive RFID Communication

This paper proposes a novel cooperative composite energy harvesting system that consists in the association of a traditional passive UHF Radio Frequency Identification (RFID) chip with an Electromagnetic Energy Harvesting Circuit (EEH-C). The objective is to exploit the i-v nonlinearity of the rectifier by applying a signal with time-varying envelope in order to improve the RF-to-dc conversion efficiency. Thanks to a multisource configuration, i.e., an RFID reader at 0.868 GHz and an external source at 2.45 GHz, the EEH-C is able to rectify the 3^rd harmonic product of the RFID chip, in addition to the 2.45 GHz signal, without compromising the RFID communication. Additionally, digitally modulated signals are used at 2.45 GHz to further enhance the harvesting efficiency of the EEH-C. From theory, simulations and measurement it is demonstrated that the exploitation of the three nonlinear effects of rectifying circuits, i.e., (i) impedance power dependency, (ii) harmonic signals production, and (iii) waveform dependency can greatly improve the conversion efficiency of the EEH-C.