Research On Angle Sensor Of Chipless RFID Tag

With the rapid development of the Internet of Things(Io T),Radio Frequency Identifica-tion(RFID)technology,which is a key technology of the Internet of Things,has received more and more attention,and has become a research hotspot for researchers.As a branch of RFID technology,the chipless RFID tag has also attracted people's interests.However,to read a chip-less RFID tag,the polarization match bewteen the reader antenna and the tag is required.Oth-erwise,the tag information measured by reader may not be obtained or be read incorrectly.However,due to the fact that the placement of objects in the actual environment is uncertain,the polarization mismatch between the tag and the reader antenna always takes place.Therefore,the study on the chipless RFID angle sensors is of great significance.This dissertation was supported in part by the National Natural Science Foundation of China under Grant 61372008,and in part by the Science and Technology Planning Project of Guangdong Province under Grant 2014A010103014,2015B010101006,and mainly investi-gates chipless RFID angle sensors.The main works include as follows:(1)A chipless RFID angle sensor based on I-shaped slot:A chipless angle sensor operating at the band of 5.6–11.6 GHz is proposed.By embedding two I-shaped slots with different lengths,which are regarded as the sensing units,the angle information of the tag is detected by measuring the amplitude of the scattered electric field of the sensing unit,thus realizing real-time sense of the rotation angle information of the proposed tag.Four coding units are etchted on the both sides of the sensing unit,consisting of three D-shaped thin-slot resonators and a U-shaped thin-slot resonator.The overall dimeniosns of the sensor are?×8×8×0.5 mm~3.With frequency shift coding,the tag can be encoded with a capacity of 8 bits.The proposed tag was fabricated and tested,the feasibility of the sensor in the actual environment is verified.When testing the amplitude of the backscattered electric field of the tag in an actual envi-ronment,it is easily influenced by environmental factors.In order to further improve the ro-bustness of tag detection,the following design emploies the resonance frequencies of the ring resonators to represent tag angle information.(2)A chipless RFID angle sensor based on ring resonators:The tag implements the angle sensing function by loading a rectangular thin slot at the“three o'clock position”of the original ring slot resonator.By measuring the the resonance frequency of resonator,the angle infor-mation of the tag can be detected.The tag is composed of three nested rings with different radii.The outside basic ring slot is adopted to encode the tag identity,and the inside two modified ring slot resonators with a phase difference of 90°is employed to transmit the angle information of the sensor tag.By using the resonance frequencies difference of the two sensing units to represent the angle information of the tag,the interference on the measurement result in the actual environment is effectively reduced,and the robustness of the tag is enhanced.The final size of the sensor is?×13×13×0.8 mm~3,which operates at the band of 3.3–8 GHz and can encode 2 bits.Finally,the fabricated tags were measured in the actual environment.The meas-ured results are basically consistent with the simulated results.In the range of 0–90 degrees,the sensitivity of the sensor is 6.1 MHz/°.In the same polarization direction,the coding and angle sensing of the sensor are easy to cause mutual interference between resonators,so the third sensor has been proposed,which the coding and sensing are distributed in different polarization directions.(3)A chipless RFID angle sensor based on dual polarization:Dual polarization is achieved by performing angle sensing in the horizontal polarization direction and tag encoding in the vertical polarization direction.The sensor unit in the horizontal polarization direction adopts the ring resonator proposed in the previous section,and the tag rotation angle information is obtained by measuring the resonance frequency of the resonator.The encoding unit in the ver-tical polarization direction uses 3 groups of C-shaped resonators.The final size of the sensor is?×11.5×11.5×0.8 mm~3,which works at band of 4–8.1 GHz.By using frequency shift coding,each coding unit can encode 2 bits,and the final tag coding capacity reaches to 6 bits.Finally,the proposed fabricated sensors were measured in the actual environment,which verifies the feasibility of the sensor.In the range of 0–90°,the sensitivity of the sensor is 8.86 MHz/°.