光纖分佈式感測技術於結構安全監測之多功應用研究

Abstract

由於現代的建築物的規模及複雜度愈來愈高，也突顯結構安全監測的重要，對於這些大型複雜的結構物，很難去預期內部缺陷的產生，而傳統的應變規的量測只能對特定點，無法瞭解結構整體的狀況。近年來光纖感測技術廣泛地用於橋樑及公共建設的安全監測，而分布式光纖感測技術的應用也是其中重要之一。 本研究對改善布里淵分布式光纖感測系統的硬體及軟體的提出四個方法，以改善量測系統，第一個是強化半激發態布里淵散射，以改善布里淵增益光譜的品質、訊號的訊雜比及空間解析度，利用極化控制器控制光極化的狀態，使50公尺的量測範圍達到30公分以下的空間解析度。其次是藉由控制探針光的衰減值，可改善訊雜比值。另外利用快速的資料擷取卡及傳輸介面控制程式，有效提升量動態量測速度。利用光切換器將本系統成功同時用於鋼結構負載、管線安全監測及智慧型壓力地板等等多功用途上。 本量測系統性能提升後，用於壓力感應地板的動態量測實驗，證明其在保全及智慧型材料上的應用潛力。在型鋼簡支樑的實驗中，由光纖感測所量得應變值與應變規所得者誤差約4%。管線簿化是一般石化廠常見的問題，以一般傳統的感測器很難測出這種小面積的缺陷，分布式布里淵感測系統在本研究實驗中，證明具有量測壓力管線內局部缺陷的能力。在動態量測方面，我們以52Hz的FM頻率切換速度，完成軌道的1 Hz動能負載測試，證明其在軌道安全監測上的應用能力，對高鐵及鐵路等的安全應用價值上是可以預期的。未來，本研究技術可提供整體結構安全監測上。

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.