Reseach On UHF RFID Anti-metal Tag With Magnetic Subatrate

With the development of information technology and the concept Internet of Things, RFID(Radio Frequency Identification) technology has played a very important position in national economic. UHF(Ultra High Frequency) RFID working in the frequency range of 860~960 MHz, is widely used in long-distance identification, due to its working distance larger than 1 m. In many practical cases, the tag antenna is posted on a metal object inevitably. It is an important technical problem to prevent UHF RFID from developing that ordinary tag cannot be read properly mounted on metal. This paper analyzed the impact of magnetic on the dipole antenna, prepared three magnetic substrate metal tags with the thickness of 2mm of the different shapes, and pointed out the research direction of magnetic substrate used in anti-metal tag.Firstly, introduced the performance parameters of the UHF RFID antenna and analyzed the antenna failure mechanism mounted on metal surface. Pattern, impedance and gain changed sharply when the tag was mounted on metal surface. Through the analysis the influences of magnetic substrate on the dipole antenna performance, using HFSS software and according to antenna theory, the paper gives the electromagnetic parameters requirements of magnetic substrate. Setting the magnetic material as substrate of the antenna can effectively reduce the physical size of the tag, but electromagnetic loss resulting in lower gain at the same time. Compared to the dielectric material, magnetic substrate can improve the gain of the metal antenna, ignoring the electromagnetic loss. The gain of antenna increases with the thickness of the magnetic substrate, when the thickness is between 0 and 0.05λ.Secondly, according to the magnetic influence on tag antenna and UHF RFID tag antenna requirements, the electromagnetic parameters of the magnetic substrate were determined. μ’ and ε’ should be less than 10. Tanμ of the magnetic material should be less than 0.1 and tanε less than 0.05 to obtain enough gain. High Q magnetic substrate makes the anti-metal tag small and thin possible. The magnetic substrate was prepared by solid state reaction method for the anti- metal tag antenna, with μ’(= 2.3)、ε’(= 6.4)、tanμ(= 0.09)、tanε(= 0.003) meeting the requirements of electromagnetic parameters of the magnetic substrate at 922 MHz for anti-metal tag antenna.Finally, designed the anti-metal tag with magnetic substrate and analyzed the tag with different magnetic substrate and different shape. Three anti-metal tag antennas were designed and prepared with thickness of 2mm. When the length of antenna is 100 mm, the maximum read distance is 3 meters. Antenna size can be reduced at the price of lower antenna gain. When the antenna size is 42 mm, 52 mm, reading distance is reduced to 1 m and 1.5 m, respectively. Complex antenna structure significantly increases energy loss at bending edged regional, requiring lower electromagnetic loss of magnetic substrate. Reducing electromagnetic loss of magnetic substrate can effectively shorten the anti-metal tag antenna thickness and length.