Research On Key Technologies Of Reliable Reading Of Near-Field Uhf Rfid System For Complex Metal Environment

Near-field radio frequency identification(RFID)technology has the advantages of fast and efficient.Compared with far-field RFID technology,near-field RFID technology also has the advantage that the reading and writing range can be accurately controlled,so it is widely used in medical treatment,storage,logistics,retail and other fields.Various metal environments are important application scenarios of near-field RFID system.This paper mainly focuses on the coverage of near-field RFID reader antenna in complex metal environment and the standing wave problem encountered by near-field RFID system in semi open metal shelf with a height of more than half of the wavelength.The main research contents and innovations are as follows:Aiming at the problem that small reading area of near-field reader antennas can not cover wide metal filing cabinets,a pure near-field broadband reader antenna with configurable reading and writing area is proposed.The antenna is based on the structure of parallel microstrip line loaded with semi ring coupling resonator,and the reading area can be expanded by increasing the number of resonators.The operating frequency of the designed 1×4 array antenna is 890-1550 MHz,and the 100%tag reading range is 360×60×32 mm3.Aiming at the problem that short reading distance of near-field reader antennas can not cover high metal containers,a near-field broadband circularly polarized reader antenna with long reading and writing distance is proposed.The antenna is based on the bent dipole structure to achieve low gain characteristics,and a sequential rotating feed network with 90 °phase difference at adjacent ports which is designed to achieve broadband circular polarization.The operating frequency of the antenna is 690-1160 MHz,and the 100%tag reading range is 500×500×500 mm3 with a coverage height of 1.5 times the wavelength.Aiming at the problem of missing reading in RFID system caused by the standing wave phenomenon of electric field distribution in high metal shelves,two 1-bit reconfigurable reflector array antennas loaded with pin diodes are proposed.The reflectarray antennas have two different working modes,and the corresponding two reflected wave phases have 180° phase difference.When the reflectarray antenna is applied in the metal shelves,the electric field wave nodes in the space can be completely staggered,and the two working modes make up for each other,so as to offset the reading blind zone caused by the standing wave,ensure that the tag reading rate of the near-field RFID system reaches 100%in 600×800×680 mm3 internal shelf space,and realize reliable reading.