Design And Implementation Of Energy Collection System In UHF Passive TAG

In recent years, radio frequency identification technology (RFID) is rapidly developing. The traditional RFID tags combined with micro-controller and sensor can set up the wireless sensor network to achieve temperature detection, biometric surveillance, movement monitoring and other various features, in addition to having the function of item identification. However, the limited battery power severely restricts the RFID system's working life and increases the maintenance costs. As a result, designing a wireless energy harvesting system to provide tag energy is particularly important.The thesis designs a tag wireless energy harvesting system based on the actual needs and performance characteristics of UHF smart tag. Designing an efficiency, low return loss tag antenna and low power consumption energy harvesting circuits is the difficulty in the system design. This thesis analyzes the characteristics of UHF tag antenna and the effect of dielectric permittivity on antenna efficiency according to theory of electromagnetic fields, and designs a dipole antenna which is suitable for UHF tags based on ordinary printed antenna. For energy harvesting circuits, the thesis uses Dickson's charge pump to design the front end voltage-doubler rectifier circuit, determines voltage series and calculates the parameters based on actual energy consumption. The circuit using Schottky diode and capacitor can efficiently convert the weak radio-frequency energy launched by reader to DC power. Then, the collected energy is stored in the capacitor for the continuous use of tag. Meanwhile, a voltage monitor is used to judge output voltage of capacitor and switch work state of the tag. After completing the circuits design, this thesis optimizes and improves the energy harvesting circuits and antennas by using Ansoft HFSS 13 and ADS electromagnetic simulation software. Finally, the results are simulated and validated.Test results show that over 1.8V working voltage for the tag has been provided by the front end energy harvesting circuits, the center frequency of tag antenna is 900MHz, the effective bandwidth is 50MHz and the S11 of resonance point is -40.8dB. The new smart tag with external sensors in this thesis can well satisfy the needs of UHF RFID tag and has strong scalability.