Research of Distributed Fiber Sensing Technology for Multifunction Application in Structural Health Monitoring
Date Issued
2010
Date
2010
Author(s)
Shen, Yu-Lin
Abstract
Structural health monitoring has gained in importance due to the continued increase in the size and complexity of modern structures. For such complex structures, it is very difficult to predict where defects will form. And since traditional strain gauges can only measure forces at specific points, they cannot, in fact, be used to gauge the status of the whole structure. In recent years, optical fiber sensing techniques have become widely used to monitor bridges and public buildings. Distributed optical fiber sensing techniques have also been used in some cases.
In this study, four techniques—both hardware- and software-based—are presented to realize an improved Brillouin distributed optical fiber sensing system. The measuring system is improved. First, enhanced semi-stimulated Brillouin scattering (SSBS) can be used to improve the signal quality of the Brillouin gain spectrum (BGS), the signal-to-noise ratio, and thus the spatial resolution. In addition, the use of the polarization state control to detect polarization changes allows an extended test region of up to 50 m and a resolution of less than 30 cm. Second, by controlling the probe value of the attenuator, this system has an improved signal-to-noise ratio (SNR). Third, a high-speed data recording interface card, together with compatible software, can be used for fast and efficient dynamic measurement. Last, the use of an optical switch allows this system to be used in several different applications, for example, load measurement in steel structures, monitoring of the pressure pipelines, pressure-sensitive floors, etc.
Experiments on the application of the improved system to a pressure-sensitive floor and for dynamic measurement clearly showed that this system can be used in security and intelligent material. In experiments using a simple supported beam, a mere 4% difference was found between measurements made by the optical fiber sensor and by strain gauges. In an experiment on a square pipe, this system accurately located cracks and measured the stress distribution. Wall thinning defects are usually localized and are difficult to be detected by traditional sensors that have a small coverage. A distributed fiber sensor based on the Brillouin sensing system was demonstrated to be able to measure the strain and detect the defect in a pipe accurately. Using fiber sensor stuck on a rail, we were able to measure 1 Hz sinusoidal dynamic strain with 52 Hz probe sweeping frequency. The correlation-based Brillouin sensor is promising as a distributed dynamic strain sensor for the applications of railway and high speed rail monitoring. Further, we propose methods to monitor structural integrity and the status of structure health.
Subjects
Structure health monitoring
Fiber sensor
Distributed sensing
Pressure-sensing floor
Dynamic measurement
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