Research On Ultra-wideband Depolarizing Chipless RFID Tag

Radio frequency identification(RFID)technology has become a research hotspot in academia,which can be applied to the Internet of Things(IoT)field and plays an important role in identity recognition,logistics tracking and intelligent sensing.At present,the RFID tags widely used in the commercial market are mainly active tags and passive tags with integrated silicon chips,which are expensive to manufacture and restrict the deployment of RFID technology.Therefore,the concept of chipless RFID tag has been proposed.Not only the encoding capacity and tag size need to be considered for a chipless tag design,but also it is important to be able to read the tag accurately in a real environment.The depolarizing technique can improve robustness of tag detection,so the research on depolarizing chipless RFID tags is very important and valuable.With the support of the National Natural Science Foundation of China under Grant 61372008 and Guangdong Provincial Science and Technology Program under Grant 2014A010103014,2015B010101006,this dissertation has studied the working principle,modeling and design procedure of ultra-wideband depolarizing chipless RFID tag.The main works as follows:(1)Acording to the principle of the electromagnetic field scattering and radar cross section theory,the working principle of chipless RFID tag is analyzed and the design procedure and working principle of depolarizing tag are summarized.(2)A depolarizing chipless RFID tag with quasi-loop resonators: A depolarizing chipless tag operating in the 4–9.5 GHz UWB band is designed.The depolarization effect is achieved by using the dipole resonant element bent at both ends.A compact structure is realized by using the nested techique to the resonators.Furthermore,the four quasi-loop resonators ensure a strong reponse in cross-polarization for an easy detection in real environments.The final size of this depolarizing tag is 21 mm × 22 mm × 0.8 mm.Besides,frequency shift encoding(FSE)method is ultilized so that a single resonator can encode 4 bits at a bandwidth of 900 MHz,and the total encoding volume can reach to 16 bits by using 4 resonators for the depolarizing tag.Finally,the prototype was fabricated and measured in the real environment.The measurement results are in good agreement with the simulation ones,verifying the theoretical design.(3)A depolarizing chipless RFID tag based on circular ring resonators with perturbation units: The tag implements depolarization effect by loading two grooves on a circular ring,and every two grooved circular rings are nested together as a group.There are three groups totally for the designed tag to cover the 4–10 GHz UWB band with a size of 55 mm × 20 mm × 0.8 mm.The FSE method is achieved by changing the radii of the rings so that each ring can encode 4 bits in 900 MHz bandwidth,and the entire tag can encode 24 bits.Ultimately,the designed tag was fabricated and tested in a real environment.The measured results are consistent with the theoretical analysis and simulation results.(4)A depolarizing chipless RFID tag for humidity sensing: Bi-directional depolarization is achieved in two cross-polarized directions(marked as V-H and H-V)using a multi-coupled Z-shaped resonator.The bi-directional depolarizing tag operates in 4.5–7.5 GHz band and has a surface size of 20 mm × 20 mm.In the H-V direction,two horizontally placed multi-coupled Z-shaped resonators serve as the encoding units of sensor,and 6-bit encoding capacity is achieved by using FSE method.In the V-H direction,two vertically placed multi-coupled Z-shaped resonators act as a humidity-sensitive unit.There are two resonant peaks in the cross-polarization direction used to detect the humidity variation,which is beneficial to reduce the humidity detection error in practical applications.The bi-directional depolarization is used to achieve spectrum reuse in the 5–7 GHz band.And the tag has depolarization characteristic,which can improve the detection robustness in the real environment.