PSI - Issue 5

K.S.C. Kuang et al. / Procedia Structural Integrity 5 (2017) 1168–1175 Dong Yang et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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acoustic emission (AE) sensors. The result shows that the proposed sensor has the potential to monitor crack initiation and propagation in real-time.

2. Crack monitoring sensor working principle

Badcock (Badcock, 1999) introduced the principle of intensity-based sensor and evaluated the basic performance of this sensor in 1990s. The optical signal variation due to the change in distance between the cleaved POFs is well discussed in (Kuang et al., 2004). Figure 1 illustrates the basic principle of measurement of the IPOFs sensor. The longitudinal separation of two cleaved POFs facing each other results in a change of the output light intensity.

Fig. 1. The schematic drawing showing the sensing principle of the IPOFs sensor

All of the POFs sensors used in this paper were fabricated by our laboratory. As shown in figure 2, the sensors were fabricated basically similar as extrinsic POFs sensors. The IPOFs sensor was fabricated by enclosing two cleaved POFs in to a specially designed PTPE tube. In contract to previously reported sensors, a small piece of 5 mm long special fibre was inserted into the cavity space (formed between the two cleaved POFs) in the proposed sensor which can take the place of air gap relied and liquid relied sensor. It will be shown that by special fibre inserted solution, the changes in the separation of the cleaved ends can be obtained clearly.

Fig. 2.Basic principle of proposed IPOFs sensor