Comparison of Performance and Stability of Different Wearable Passive UHF RFID Tags in Body- worn Configuration.

摘要

RFID or Radio frequency identification is an unsymmetrical radio communication protocol, where uplink (from tag to reader) communication is carried out with backscattering modulation. The foundation of Schottky diodes to CMOS processes provided the means of passive RFID, i.e. transponder or tags without a battery, at ultra-high frequencies with justifiable low cost and read range. The thesis studies the different types of tags on human body and see the performances and their stability. Performance is the measurement of read range of the different tags and stability shows how stable the tags behave on human body. The human body is different in size and shapes. So, it was interesting to see how tag behaves on different types of people.They solution for this thesis was designed in three ways. i) anechoic chamber measurements ii) human body with the tags in anechoic chamber measurements iii) analysis of tags behaviour in MATLAB. In order to finish the first step, three types of RFID tags were developed in the lab and measured their theoretical read range. Tested tags were a) dipole RFID tags b) slotted patch RFID tags and c) square slotted RFID tags. For second task, tags putted on different human body and measured their response as read range. The human being are different in sizes so responses were different in them. Lastly, all the result was analysed by MATLAB. Analysis was carried out in three conditions. They are i) line of sight measurements ii) 45-degree right shift measurements and iii) 45-degree left shift measurements. For deep analysis of the thesis work, investigation was emphasized on the vertical and horizontal polarization. All the mentioned steps were analysed in the vertical and as well as in the horizontal plane. The LOS condition is straight forward such as measure the human body containing tags and in the line of sight with the reader antenna. The other two were somewhat tricky because of different angle separation such as ‘45’ degree right or a left shift. Thanks to geometry which has ease this problem. It has seen that in case of close proximity with human body the RF wave tends to lose its energy so the tags could not operate in regular efficiency. It has also observed that when tag placed on air medium the average read range is around 5m for dipole RFID tags and for the slotted patch it is around 4m. But when tags were attached to the human body upper back side the read range was 3.5m for dipole RFID tag and 3m for slotted patch RFID tags. This change of read range between air medium and human body-worn configuration is due to the human body. Human body is a lossy medium. 70% of human body weight is water and presence of water RF waves decreases its performance. The high dielectric constant and loss tangent is due to human body effects. Because of this problem wearable tags lose its received power from the reader in to the human body. It has also noted that centre frequency has shifted in body-worn configuration. It has also observed that in different angle RFID still working. There was noticeable amount of change in centre frequency due to human body interaction. This is because of human body is not symmetrical.