Research And Design Of An Anti-Metal Passive UHF RFID Tag

In recent years, ultra high frequency radio frequency identification technology has become more mature and their application scenarios are continuously enriched, therefore passive tags used in the metal surface are also increasing, such as container surface. However, due to the ideal boundary effects conductive metal surface so that the original radio frequency identification system is not working properly, resulting in significantly reduced recognition range, so the industry needs to design a special tags can be used on the metal surface, which is named the anti-metal tag.Key indicators of anti- metal tag is the furthest recognition distance, which is determined by both the tag gain and impedance matching. C urrently, the industry lacks high gain anti- metal tag. And in practice, measuring the input impedance of the antenna and the input impedance of the passive chip also has some problems, resulting in impedance matching uncertainty. Therefore, to design a passive tag with a high gain and better impedance matching contains certain challenges and practical significance. In addition, tag cost is an other hand key factor to decide whether tags can be commercial. The current anti- metal tag in material cost or manufacturing cost is still too high compared to commercial ideal cost. Therefore, in order to solve the above problems, this paper seeks to design a high gain, better impedance resistance, far identified and low-cost anti- metal tag.First, this paper starts from the perspective of the basic principles to analyze the impact of the traditional tag given by metal plane and factors to suppress the above influence. Thus, the present paper reaches the conclusion that the introduction of the metal surface produces a standing wave effect and impedance transformation effects. These two effects influence the tag's gain and the tag's impedance matching, respectively, so that the tag's the farthest identification distance lowered sharply to abnormal operation. Using the expanded metal ground and using the thickened dielectric substrate can reduce the impact of the traditional label given by the metal surface effectively.Secondly, based on self-designed passive chip with national standards, this paper carries out the anti- metal tag design. According to a new method proposed in this paper to measure the input impedance of the passive chips which is given to the tag antenna as its input impedance target value when the anti- metal tag is designed. After that, this paper carries out the antenna selection analysis, structural analysis, transmission line model analysis, cavity model analysis as well as simulation by software HFSS successively, and determines gradually the structure and the size of the tag which the simulation performance results meet design specifications.Finally, the paper uses modern technology to manufacture the anti- metal tag designed previously, then in accordance with the principle of “cavity reflection” proposes an improvement program on this tag and gives the improved performance values. According to a new method adopted in this paper, this paper measures the input impedance of the tag antenna, the measurement results and the target value is consistent with the simulation results. After that, this paper conducts a comprehensive test of the tag, including the anti- metal performance. Test results are generally consistent with the the estimated value of the simulation, and demonstrate this tag possesses excellent performance. When this tag is on a metal surface,-10 dB bandwidth covers 920-925 MHz which is required by the protocol, gain is about 2.4d Bi, and the farthest identification distance within the bandwidth of the protocol requirement is more than 6.5 meters, it also meets all the design requirements and has excellent anti-metal performance.