Papers by Keyword: Fiber Bragg Grating (FBG)

Abstract: The real-time monitoring technologies of smart civil structure based on detecting picometer-scale wavelength shift of fiber Bragg grating (FBG), including the wavelength demodulation technology of FBG, are researched extensively at home and abroad. In the paper, using the technologies of wavelength division multiplex (WDM) and time division multiplex (TDM), fiber Bragg grating (FBG) sensor network was built for monitoring smart structure health condition. Based on SOPC (System on Programmable Chip) technology and fiber comb filter, a high-speed and high-precision wavelength demodulation scheme of FBG sensor network was proposed. The optical system and hardware circuit for demodulation system were designed specifically. To improve the accuracy of demodulation system of FBG, a constant temperature channel of the demodulation system connected with a fiber comb filter, which offered reference points to calibrate the Bragg grating center wavelength. Based on 32-bit soft-core processor NoisⅡ, the embedded system collected and processed the photoelectric signal voltage transformed to rectangular voltage pulse. The upper computer displayed dynamically the FBG wavelength demodulation process and calibrated the Bragg grating center wavelength. The experiments of FBG wavelength demodulation and health monitoring of smart structural embedded fiber Bragg gratings were done. Experimental results show that, the FBG wavelength demodulation method can be used to demodulate the FBG wavelength with high speed and high precision (± 2 pm), which can be used extensively in large-scale multipoint monitor engineering, and the strains of the smart structure can be measured accurately.

Abstract: The deformation is an important parameter in structural health monitoring, and a conjugate beam method based on long-gauge fiber Bragg grating distributed strain sensing techniques is proposed to obtain the deformation of a structure. Some experiments are carried out to study the accuracy of this method using a four point bending RC beam under a step loading manner. The deformation obtained with the proposed method agrees well with those obtained with the conventional dial gauge in low loading steps. In addition, some measure is put forward to calibrate the proposed method and improve its accuracy at high loading steps, especially after the initiation of concrete cracks.

Abstract: In order to improve the accuracy of measurement results, we should do our best to reduce the optical loss while welding FBG Sensors and adopt appropriate bonding technology. Taking simple tools and suitable approach can also achieve good result. We take three steps while welding FBG sensors, the steps are manufacture end face, welding, and heat shrinkable. Manufacturing end face of a fiber is the key step among them. It is important to adopt the sequence diagonal welding method and use a damp cloth to cool the other parts of the sensor while welding which can increase the accuracy of measurement. Use pen-made red light to check the fiber joints.

Abstract: Fiber Bragg grating and resistance strain gauge have been used to test the stress change in key parts of structure of 61t-55m quayside container crane under the same testing conditions. The testing data and stress-time history diagrams obtained by the resistance strain gauge and fiber Bragg grating have been analyzed. The results verify good real-time property and high reliability of the structural health monitoring system based on fiber Bragg grating system.

Abstract: The cracks have emerged on the second lining of right tunnel for three months after tunneling in the Xin Chang Tunnel. The maximum crack depth is 264.0 mm which is explored by a RS-ST01C type ultrasonic tester. A fiber Bragg grating strain sensor is developed for measuring the surface strain of second lining. By converting the deflection of structure into the strain of displacement telescopic gauge, a fiber Bragg grating is mounted on two ends of gauge where suffers the strain, and as a result its Bragg wavelength will be shifted. The strain sensitivity and temperature sensitivity of the grating sensor are separately 0.677×10^-6/ and 0.968×10^-5 /°C. Grating sensors are installed on the corresponding linings according to the crack distribution. In an observation period of 51 days, the measurement results indicate that the lining cracks are derived from the tilted pressure of surrounding rock. After a backfill period of 29 days, the tunnel structures are gradually tending to be stability in the following operation period of 429 days.

Abstract: The influence of grating period and length of Photonic Crystal Fiber Bragg Grating on delay is investigated by using numerical simulation method and the coupled mode theory. The result shows that grating length and period has remarkable impacts on the delay. The maximum value of the delay can be obtained by parameters optimization, which is 52ps occurs at the grating length of 1.06cm.

Abstract: Power transmission tower is an important part of power transmission equipment. The tower foundation is suffered by landslides, debris flows, erections of foundation settlement and so on. The power transmission tower near Yanjin transformer substation is selected to be measured. By using fiber Bragg grating (FBG) earth pressure sensor, the earth pressure of tower foundation is measured. The long-term monitoring data indicate that the #1 sensor daily variations amplitude of earth pressure is 7.22KPa, and the #2 sensor daily variations amplitude of earth pressure is 4.69KPa. In the 479 days, the rangeability of average data is 61.55KPa in sensor #1 and 64.05KPa in sensor #2. Compared with the local precipitation, the earth pressure of tower foundation is seasonal change. According to the history data, the warning threshold value is set as 280KPa.

Abstract: This paper reports on an experimental program of work which investigates the use of fibre Bragg gratings (FBGs) for the measurement of surface strains during full-scale structural testing. The test article was an ex-service F/A-18 wing attachment centre barrel (CB). The CB has three main structural bulkheads whose function is to carry wing loads into the fuselage. Two FBGs were surface mounted to each bulkhead on the starboard side with electrical resistance foil strain gauges bonded to symmetric locations on the port side of the structure for comparison. The FBGs were fabricated during the fibre draw process and were then packaged in a composite tape for secondary bonding to the structure under test using a standard aerospace qualified strain gauge adhesive. The centre barrel was subjected to a series of load surveys comprising 50%, 70% and 100% of the maximum spectrum load amplitude and low constant amplitude (8% of maximum spectrum load) cycling during thermoelastic stress analysis surveys prior to the initiation of variable amplitude accelerated fatigue spectrum loading until structural failure. The experimental data shows good agreement between the electrical-resistance foil and optical gauges when the loading is symmetric with additional detail provided by the optical gauges which had a higher sampling rate. These results confirm the potential of FBGs to provide detailed experimental strain data from across the structure without the associated complexity of wiring and installation often associated with electrical foil gauges.

Abstract: Current study presented a simple, temperature-insensitive fiber Bragg grating (FBG) force sensing system. It is based on an optical intensity modulation scheme with a corrugated long-period fiber grating (CLPFG) filter. The temperature effect of signal variation is about 6%. Through FBG temperature compensating scheme the average temperature sensitivity is improved obviously (0.06 mV/°C).

Abstract: A novel gas flow sensing probe based on silver-coated Fiber Bragg Grating (FBG) is proposed. A square hole was fabricated in the middle of a capillary stainless steel pipe. A silver-coated FBG sensing probe was fixed up between the hole. The diameter of the silver-coated FBG sensing probe is only 0.125 mm, with the PVC materials deposited around the surface of the both ends with a diameter of 0.9 mm. Simulations on different packages of sensing probe were carried out via Finite Element Method (FSM). Results of the simulations reveal that the sensing probe of the capillary stainless steel pipe with a diameter of 3 mm and the square hole with a length of 12 mm can provide the best performance.