分散式光纖布里淵散射量測系統之建置

Abstract

由於結構物的大型化、複雜化，使得結構健康的監控變得越來越重要。目前已有很多監控系統實際應用的資料，但由於結構未來損害的位置很難預測，而傳統式感應器僅能在特定位置測量到結構的反應狀態，所以很難反映出結構體的真實狀況。最近光纖感測技術已經廣泛地被運用在橋梁和公共工程的監控方面，有些甚至已具有分佈式的感測能力。 本論文最主要目的就在於建立一個以相關性光纖布里淵散射為基礎的自動化光纖量測系統，以連續地測量在光纖任何位置的靜態或動態反應，並提供足夠高的空間解析度。藉由自動化儀器控制及定位系統的輔助，本研究已開發了可快速啟動(約2分鐘)的量測系統。 本論文藉由三項硬體改善技術來提高量測系統之性能。首先，將可調式的衰減器增加到測量系統中，使探測波的強度維持在較佳的狀態，如此可獲得較好的訊號雜訊比，並避免因泵波能量消耗所造成的量測誤差。其次，利用極化控制器去維持最佳化的極化狀態，以減少因為光波極化波動所造成的不穩定。第三，為了加大量測的範圍，本研究發展出一個極化隔離器，藉由這個隔離器的使用，可將量測的範圍提高許多倍。 本論文藉由簡支梁、物質特性測試和裂縫偵測測試，來驗證量測系統之性能。系統不但能提供應變和溫度的量測值，同時能夠提供代測物的定位資訊。在空間解析度2公分的情況下，應變量測可準確到100με、溫度量測可準確到1∘C。除此之外，藉由訊號處理技術進行布里淵光譜頻散的重建，可進一步提高空間解析度到6 mm。 本研究藉由新的動態量測方法的開發，來克服系統反應速率不足的問題，使本系統也可以運用到動態測量。藉由此量測方法的運用，本測量系統在動態測試中可以準確地量測到高達7 Hz的動態應變變化。 除了應變與溫度感測器外，本研究還設計了許多感測器，包過位移感測器、角度感測器和傾斜感測器。藉由此複合感測器的架構，可以提供量測系統更大的彈性，並滿足結構物健康監測的實際需求。

As structures become bigger, taller, and more complex, the health monitoring of structures becomes more and more important. Many monitoring systems have been proposed in the literature. However, due to the characteristics of conventional sensors, structural response can only be measured at specific locations. Since it’s very difficult to predict the future damage locations of the structure, the monitoring systems usually fail to reflect the conditions of the structures. Recently, optical fiber sensing techniques have been widely adopted in the monitoring of bridges and public works, and some of them have the capacity of distributed sensing. The goal of this dissertation is to establish an automatic optical fiber sensing system based on the Brillouin optical correlation domain analysis (BOCDA) such that static and dynamic response can be measured continuously at any point along the fiber with high spatial resolution. By the aid of GPIB and locating schemes, a quick start (about 2 minutes) measurement system has been developed. Three major hardware modifications were made to the BOCDA system to improve the performance. First, an attenuator was added to the measurement system to keep the power level of the probe at a suitable level such that a better signal to noise ratio can be attained and pump depletion can be avoided. Second, a polarization controller was applied to keep the polarizations in optimal states such that the fluctuation of the polarizations of the lightwaves can be prevented. Third, in order to enlarge the measurement range, a polarization isolator was developed. With this isolator, the measurement range could be multiplied several times. A simple beam test, a material property test, and a crack detection test were conducted to verity the performance of the measurement system. It is seen that the system can provide not only strain and temperature but also the location information of the measurand. The strain and temperature measurements of the system are accurate up to 100me and 1°C, respectively, with a spatial resolution of 2 cm. The spatial resolution was further improved by a signal processing technique to reconstruct the broadened Brillouin spectrum. A limiting spatial resolution of about 6mm was realized. The monitoring system is also applicable to dynamic measurement. A measurement scheme was developed in this study to overcome the problem of low response rate. With the new measurement scheme, the system is able to measure the strain accurately in a dynamic test with a vibration frequency up to 7 Hz. Finally, several sensors were devised in this study other than strain and temperature sensors, including the displacement sensor, rotation sensor, and inclination sensor. Such multi-sensor architecture provides more flexibility and meets the requirements of structural health monitoring in real applications.