The influence of structure uniformity on resonant frequency of ultra-high frequency radio frequency identification tag thread With normal mode helix dipole antenna

The stable performance of ultra-high frequency radio frequency identification (UHF RFID) tag thread with normal mode helical dipole antenna (NMHDA) was required for industrialized application. The ununiform helical pitches and helical radiuses caused by the unstable tension in the preparation process and material properties of carrying yarn probably deteriorate the performance of UHF RFID tag thread with NMHDA, while previous work focused on the properties of UHF RFID tag thread with uniform structure by finite element simulation. This work conducted numerical experiments with the actual statistical distribution of helical pitch and helical radius, i.e. normal distribution, and discussed the influence of the distributed parameters on resonant frequency. And then, the relationship between structure uniformity and resonant frequency was explored. Furthermore, the relationship was put into practice of the design of UHF RFID tag thread with stable properties. The results show that the fluctuation of resonant frequency first decreases and then increases with the increase of the mean helical pitch (S me ), and the resonant frequency decreases with the increase of the standard deviation of helical pitch (S st ) and that of helical radius (r st ). When the reactance of helical coil linearly changes with helical radius, the mean helical radius (r me ) has a negligible effect on the fluctuation of resonant frequency. The importance of the factors for the resonant frequency conforms to the following order: r me >S st >S me >r st . Additionally, the stable reading range of prototype (14.13 ± 0.06 m) demonstrated the practice of these results in the design of UHF RFID tag thread with NMHDA.