An embedded fiber optic sensor based on the photonic crystal fiber is proposed to measure the transverse stress in composited material for structural health monitoring. The sensing principle has been analyzed and validated by experiments. The 0.1%F.S high precision calibration device has been designed to indicated that linear correlation between the wavelength shift of Sagnac loop and pressure, and the good performances of sensor, such as the sensitivity coefficient is 0.1285nm/N, linearity is accessible to 1.02%F.S, maximum error is 3%F.S. Other experiments have been done by a material testing machine on the sensor, which have shown that the sensitivity coefficient is increasing with sensing length but immune with the shape of sensor. The sensor will be suitable for solving the problem of high precision online pressure monitoring in some complex structure health monitoring.
Pressure method using polarization-maintaining photonic crystal fiber (PM-PCF) as sensing element based on Sagnac interferometer is proposed to monitor inter layer pressure in especial compact structure. Sensing model is analyzed and test system is set up, which is validated by experiment. The birefringence can be modified by the deformation of PM-PCF under transverse pressure, realizing pressure measurement by detecting the wavelength shift of one specific valley from output of the Sagnac interferometer. The experiment results show that the output interference fringes were shifted linearly with pressure. The dynamic range of 0 kN ~10kN, sensing precision of 2.6%, and pressure sensitivity of 0.4414nm/kN are achieved, and the strain relaxation phenomenon of cushion can be observed obviously. The sensor has better engineering practicability and capability to restrain interference brought up by fluctuation of environment temperature, which temperature sensitivity is -11.8pm/°C.