The ultrasonic (US) wave detection and an acoustic emission (AE) linear location system are proposed, which employ fiber Bragg gratings (FBGs) as US wave sensors. In the theoretical analysis, the FBG sensor response to longitudinal US wave is investigated. The result indicates that the FBG wavelength can be modulated as static case when the grating length is much shorter than US wavelength. The experimental results of standard sinusoidal and spindle wave test agree well with the generated signal. Further research using two FBGs for realizing linear location is also achieved. The maximum linear location error is obtained as less than 5 mm. FBG-based US wave sensor and AE linear location provide useful tools for specific requirements.
A novel resonant fiber Bragg grating(FBG) based acoustic emission(AE) sensor with relocatable, strain-insensitive and enhanced sensitivity structure is demonstrated for structure health monitoring(SHM) in this paper. With one end of the sensing FBG bonded to a polyimide(PI) plate acoustically coupled with the investigated structure via couplant and the other end free, the sensor can be easily redeployed around the monitored structure surface and get rid of the interference from the strain applied on the monitored structure. Experiment has been conducted to verify the characteristics of this FBG-AE sensor, whose results show that the sensor is insensitive to mechanical strain applied on the monitored structure. It is also shown experimentally that the sensitivity is enhanced by about 1.2 times than the conventional design, while the novel sensor possesses good resonant frequency response to the standard AE waves.
A fiber Bragg grating temperature sensor network was designed to implement the real-time health monitoring of the aluminum reduction cell. The heat transfer process was simulated using software ANSYS, and an on-line shell monitoring system was established based on optical sensing technology. According to aluminum reduction cell heat transfer theory, the 2D slice finite element model was developed. The relationship between shell temperature and cell status was discussed. Fiber Bragg grating (FBG) was chosen as the temperature sensor in light of its unique advantages. The accuracy of designed FBG temperature sensors exceeds 2℃, and good repeatability was exhibited. An interrogation system with 104 sensors based on VPG (volume phase grating) filter was established. Through the long-term monitoring on running state, the status of the aluminum reduction cell, including security and fatigue life could be acquired and estimated exactly. The obtained results provide the foundation for the production status monitoring and fault diagnosis. Long-term test results show good stability and repeatability which are compatible with electrolysis process.
