Papers by Keyword: FBG

Abstract: In this paper, possibility to detect damage on post-tensioned concrete girders was investigated through an experimental program with 6 m long specimens containing smart tendons where FBG (Fiber Bragg Grating) sensors were embedded. Total six specimens were fabricated and tested, and test variables were prestressing tendon’s profile and web thickness. All the specimens were subjected to 3-points loading, and they exhibited shear failure. Through the test, it was observed that tendon strains were successfully measured through FBG sensors regardless of the test variables. It was also observed that tendon strains within the pure span significantly increased while ones nearby the anchors beyond the pure span were constant. When the specimen was cracked, FBG sensors nearby cracks showed relatively drastic increase on tendon strain. Since strain variation along tendons cannot be detected by conventional equipment such as a load-cell, the test results indicated that actual tendon strains can be easily measured with FBG sensors. These results showed that FBG sensors can be useful to check whether prestressed concrete members were significantly damaged. In addition, it is expected that FBG sensors can be helpful on more reasonable maintenance of PSC girders.

Abstract: Most optical hydrogen sensors are based on light intensity measurement and light intensity detection is vulnerable to the light source output and the optical fiber arrangement. To overcome the shortcomings, an optical fiber based sensor based on fiber Bragg grating (FBG) technique which is capable to measure the concentration of hydrogen dissolved is described in this paper. To examine the availability of monitoring initial hydrogen generation, a needle-to-plate partial discharge (PD) model was setup in the lab. The results between wavelength shifts of optical hydrogen sensor well agreed with conventional dissolved gas analysis (DGA), proving a potential utilization in the detection of dissolved hydrogen in power transformer.

Abstract: FBG (Fiber Bragg Grating) is a new type of optical passive device which can be used in sensing field. This paper demonstrates the feasibility and effectiveness of FBG as the new method of strain measurement, and improves the measuring precision. Based on the strain sensing property of FBG, the study adopts the differential method of double FBGs to make temperature compensation, and conduct the contrast experiment with resistance strain chip. The experimental results show that strain measurement based on FBG agrees well with theoretical calculation. The measurement error: no more than 1%, linear fitting correlation coefficient: almost 1, linearity: 0.17%, sensitivity: 7.92, hysteresis error: 0.347%, repeatability error: 0.333%. The results show FBG’s performance are superior to resistance strain chip, especially in aspect of measuring precision. Therefore, we can conclude that FBG is a feasible and effective method of strain measurement.

Abstract: Peak reflectivity is a key reflected index of FBG, and it has great effects on the FBG application characteristic in sensing and communication fields. Theoretical and simulation methods are applied to study the cross influence of multiple parameters, such as grating length, grating pitch, and refractive index modulation depth, on FBG peak reflectivity. Research results can provide system recommendations for adopting proper parameter combinations according to practical manufacturing condition and actual demands.

Abstract: Research of FBG temperature sensing network base on WDM combined with spatial division multiplexing. Theoretical analysis and numerical simulation proves that the scheme is feasible, and the system has relatively higher measuring accuracy, which realizes the temperature dynamic measurement in large space, forming temperature sensing network.

Abstract: Fiber Bragg Grating (FBG) sensing technology is widely used in detection of temperature, strain and etc. Now the application of FBG sensor is limited below 200°C. Application over 200°C is still an engineering challenge since no suitable FBG strain gauge. In this paper, FBG strain gauge structure which consists of three FBGs is designed and fabricated based on the theoretical strain and stress analysis. This strain gauge can be used for the real-time high temperature strain monitoring situation. The elastic high-temperature alloy (10MoWVNb) is chosen as the substrate. The three FBGs with a similar performance are fabricated on the substrate by high-temperature glue. Among the three FBGs, FBG1 is used for the horizontal strain monitoring, FBG2 is used for the longitudinal strain monitoring, and FGB3 is used for high temperature cross-sensitive compensation. The fabricated high temperature FBG gauge is demonstrated suitable for high temperature strain monitoring by experiment.

Abstract: This paper is for real-time monitoring sag problem of overhead lines, modeling two kinds of models with the state equation of catenary line and parabolic method, which are based on fiber grating sensing technology and take advantage of the conversion relationship of overhead line length between different states. The performance comparative analysis is carried out between the two models and currently relatively mature angle method. Experimental measuring results show that under the same conditions, the monitoring results of two models are very near to the monitoring results of angle method. But relatively speaking, monitoring results of the catenary model are more accurate. The accuracy of models can meet the project requirements and two models both can monitor overhead lines sag effectively in real time.

Abstract: With finite element method, the numerical model of the E-type diaphragm was built in this paper. Based on the model, we got the shear strain law of the E-type diaphragm surface under uniform pressure. Taking it as elastic element and the FBG as sensing element, we made a FBG pressure sensor and obtained the experiment result. The result fit well with finite element simulation value. It shows that the finite element model in the paper is reasonable and effective. The model can be used to design and optimize the sensor.

Abstract: Nowadays, fiber optic technology has been used in sensing. Using the distributed optical fiber sensing technology in the landslide monitoring, the linear strain distribution information of the whole landslide can be obtained, and adopting the Fiber Bragg Grating sensing technology in the landslide monitoring, the key pot strain and displacement information can be gained. This paper firstly reviews the basic principle of optical fiber sensing, and then describes the optical fiber sensing real-time monitoring system by combining with FBG technology, BOTDR technology, database technology and web server technology, and finally presents a field application experiment using the real-time monitoring system in Ripley landslide in Canada. The experiment indicated that the real-time monitoring system can be realized real-time monitoring of FBG and BOTDR for landslide, and the experience can be extended to other landslide.

Abstract: The wavelength of Fiber Bragg grating (FBG) sensor signal demodulation simulation system based on the quasi-linear relationship between the transmission side band of optical filters and wavelength was established by the simulation software of MABTLAB. The simple system only consists of broadband source, sideband optical filters, couplers, a FBG, data acquisition and processing system. The relationship between the information of FBG central wavelength and the transmitted light intensity of sideband filter were obtained when the alternating and gradually varying signal applied to the FBG sensors, respectively. The FBG wavelength demodulation can be achieved by sideband filtering, and results are consistent with the theory.