The microstrip patch antenna sensor is a novel sensor used for structural health monitoring which can measure metal structure’s crack defects in a wireless manner. However, it is difficult to identify the reflected signal from the signal of antenna sensor. The radio-frequency identification (RFID) antenna sensor, which combines RFID technology and the microstrip patch antenna sensor, can solve the measurement problems that are difficult to the conventional wireless testing technologies. In this study, a dual-chip RFID antenna sensor was designed. The influence of the wireless testing method on the monitoring results of crack defects was investigated by tests, including the wireless tests of resonant frequency and the crack sensitivity tests. The tests results revealed that the antenna sensor had good wireless testing performance with regard to the metal structure’s crack defects. And the maximum of wireless identification distance reached 1.96 m.
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In your measurement setup, the relationship between the crack length and the resonance length was determined using the constant distance variable power method (see Fig. 6b). The resonance length and the sensitivity were measured for a crack length respectively of 4, 8, 12, 16 and 20 mm on a ground plate made of 6061 aluminium with dimensions 500 x 300 x 2 mm and an RFID antenna sensor attached to this plate in a crack-free region.
Is there an influence between the location of the cracks in relation to the location of the RFID antenna sensor on the resonant length, sensitivity and identification distance of the antenna sensor ? If yes, what is the maximum permissible distance between a crack and the RFID antenna sensor at which this measurement principle can still be applied?
We are so glad to hear from you. Thanks very much for your comment to our paper.
In our measurement setup, the constant power variable distance method was used for which is simple in operation and low in requirements for test equipment.
According to the reference 1 from our research group, when the relative location between the cracks and the RFID antenna sensor is different, the current density distribution on the ground upper surface is different, which directly leads to that the resonant length and its increment are different. The sensitivity (frequency shift caused by per crack length) is determined by the resonant length increments, therefore, the resonant length and the sensitivity are both influenced by the relative location between the cracks and the RFID antenna sensor. The identification distance is directly determined by the return loss of the S11 curve which is influenced by the crack propagation. All in all, there is an influence of the relative location between the cracks and the RFID antenna sensor on the resonant length and the sensitivity but not on the identification distance.
In our setup, the RFID antenna sensor was pasted directly on the aluminum plate with cracks, and the maximum permissible distance between the sensor and the RFID reader was 1.96 m.
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1 Ke, L; Liu, Z; Yu, H. Characterization of a Patch Antenna Sensor’s Resonant Frequency Response in Identifying the Notch-shaped Cracks on Metal Structure. Sensor 2018, 19, 110, doi:10.3390/s19010110.