Research On Mechanism Of Resonance Frequency Based On Passive RFID Antenna Sensor

Structural health monitoring (SHM) is one of methods for automatically monitoring structure health status, it is one of the key technology to ensure the safety of the structure. Traditional monitoring methods have lots of disadvantages, such as high cost of cable and maintenance, complexity of layout and manual operation. This paper is going to develop the RFID (Radio Frequency Identification) strain sensing technology that is passive, wireless, high reliability and low cost. So this paper focuses on studying the mechanism of resonance frequency when RFID antenna sensor straining.Firstly, with theoretical derivation, we get the conclusion that there is the good linearity between normalized resonance frequency shift and the strain. Then, we design folded patch antennas with coaxial line feed or microstrip line feed with HFSS.Their original resonance frequency is 2.45GHz. With the simulation and experiments,the probability that folded patch antenna can be applied as strain sensor is proved.Aiming at the existing problem of antenna design and experimental process, the paper puts forward methods to improve the experiment.Secondly, a quarter-wave length folded patch antenna with via holes is adopted as the passive wireless strain sensor. With theoretical derivation, modeling, simulation and experiments, it is proved that sensing sensitivity in longitudinal strain is better than that in transverse strain. This part focuses on analyzing the difference of strain sensitivity between simulation and experiment. The strain transfer ratio and the possion effect is taken into consideration to explain the opposite effect. Finally, the strain sensitivity of resonance frequency shift and the strain is obtained, which is-0.8652.In order to promote the practical application of antenna strain sensor, this paper designed a patch antenna with via holes and coaxial line feed. A wireless measurement scheme is designed to study the relationship between measuring distance and resonance frequency. According to the study, the best wireless measuring distance is 6 cm. Strain measurement experiment with distance of 6 cm show that, during the wireless measurement, there is the good linearity between resonant frequency deviation rate and strain as well.