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Title: UHF RFID tags mountable on metallic and challenging objects
Author: Pour Sohrab, Abed
ISNI:       0000 0004 7428 6603
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2018
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Radio frequency identification (RFID) technology has been developing rapidly during the past years. It has been replacing optical barcodes and has found many applications beyond tagging and tracking objects. Despite their undeniable advantages, passive RFID tags working in the ultra-high frequency (UHF) band are sensitive to the host material and their performance is affected when attached to different materials. Although there are robust tag designs, the fabrication is costly. The motivation of this research is to study the effect of the challenging materials on the tags and find solutions for robust cost-effective designs. Liquid bottles are one of the challenging objects for RFID tags. The study on the equivalent circuit of a typical tag which is basically a dipole antenna shows the liquid increases the loss resistance of the antenna and affects the impedance matching between the antenna and the chip. Two extra arms are added to the antenna in the suggested solution to alleviate the destructive effect of the liquid. The read range of the tag is improved without increasing the size of the design. Study of the detuning effect shows that the capacitances in the antenna are the most sensitive elements. The presented theoretical analysis reveals that less capacitance in the feed point and more capacitance in the dipole arms lead to more robustness of the tag performance to the host material. Based on this finding a low cost 3D tag is designed. The label-type dipole tags offer desirable uniform radiation pattern but are not functional on metallic objects. On the other hand the patch antennas are not efficient on non-metallic objects in terms of read range and radiation pattern. A novel hybrid tag is proposed which has the advantage of both types of antenna. The simple groundless design works in two modes. It acts as a dipole antenna in off-metal mode and a patch antenna in on-metal mode. The measurement result shows an outstanding performance on different materials. Protecting the antenna from metallic background using an artificial ground plane composed of periodic structures is a practiced method. Mushroom unit cell is the most common structure used as artificial ground but the need for via increases the fabrication cost. It is shown that the fabrication cost can be reduced by eliminating the via and having a uni-planar structure. There has been many works in the literature proposing tag designs robust to the host material but what makes this works distinct from the previous works is in depth study on the effect of the challenging material on the performance of the tag antenna and identifying the main reason of the read range degradation for the first time. The findings of this study can be used for designing cost effective tags with improved read range. Analysis of the different parts of the tag antenna and their sensitivity to the host material is also performed for the first time in this thesis. The result of this study shows how the shape of the tag can determine the robustness to the host material. In addition to novel tag designs proposed in this thesis, a straightforward strategy for designing optimum tags is also introduced. This novel method helps the tag designers to modify the primary design step by step and reach the optimum result in a short time.
Supervisor: Huang, Yi ; Shen, Yaochun Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral