Study on the coupling effect characteristics of multiple RFID sensors for crack monitoring in aluminum alloy structure

Purpose The aircraft skins are prone to fracturing, leading to serious safety hazards, due to manufacturing defects, overstress, fatigue and harsh environments. Therefore, a method with high reliability, low cost and simple networking was needed to achieve structural life evaluation through continuous monitoring. This paper aims to investigate using a sensing system consisting of densely arranged multiple tags for crack monitoring in aluminum alloy structures. Design/methodology/approach In this paper, a sensing system was composed of four tag arrangements, and the variation of gain and impedance caused by the coupling effect among tags was analyzed via simulation. The reliability of sensor systems for crack detection was studied by constructing a test platform. Findings The simulation results showed that as the crack depth in the coverage area of Tag 1 increased, the real part of the impedance of Tag 1 remained constant. In contrast, the value of the imaginary part tended to increase, while the impedance values of other tags remained unchanged. The gain of Tag 1 decreased, while the gains of the different tags remained unchanged. The test results indicated that the backscattered power tended to decrease as the crack depth increased when a single tag was placed on the surface of the aluminum alloy structure. The backscattered power of Tag 1 increased, while the backscattered power of Tag 4 remained constant when multiple tags were placed. Multiple tags were affixed to the surface of the aluminum alloy structure, leading to mutual coupling between the antennas, which decreased the sensors’ detection sensitivity. Originality/value This paper explores using multiple tags for crack detection in aluminum alloy structures. The consistency of the feature results improves as the relationship between the projection coefficient of the second principal component and the crack depth is established. This paper provides a foundation for utilizing multiple tags for crack detection on the surface of aluminum alloy aircraft skin.