光纖光柵於應變梯度量測的理論分析與應用於形狀記憶合金的特性研究

Abstract

光纖由於其優良的光傳性質，一直以來受到通訊領域的矚目。而隨著光纖光柵的發展，也促使近年來光纖感測技術的研發，其中又以布拉格光纖光柵感測器最受重視。因此，本文主要在於探討布拉格光纖光柵感測器相較於其他感測器的優勢。 布拉格光纖光柵應用於機械領域量測上，大多著重於均勻應變場的量測或定點式的量測，並探討其頻譜飄移對應於布拉格光纖光柵感測器量測到的平均應變。而本文則推廣布拉格光纖光柵感測器應用於量測線性應變場的變化量，主要是由頻譜面積的變化來探討光纖光柵所負載的應變梯度，並驗證其與模態耦合理論得到的結果，且藉由光功率計的轉換，即可及時得到布拉格光纖光柵感測器受應變梯度變化所造成的頻譜面積變化情形。 由於布拉格光纖光柵在幾何特性上的優勢即為細長、體積小且具可撓性，因此本論文將探討其是否可量測到其他感測器幾乎無法量測的細弦結構，結果顯示布拉格光纖光柵感測器不僅對應變具有高度靈敏性且可量測比自身直徑細小的結構。本文並將其感測能力延伸應用至形狀記憶合金絲做同位配置的量測，以此解決形狀記憶合金難以量測其應變而需要利用自感應特性建模的困難與不夠準確的問題。

Since optical fiber has several excellent properties of optical propagation, it has been noticed in the signal processing and communication field for a long time. With fiber grating’s development, fiber is also utilized to mechanical measurement, and Fiber Bragg grating (FBG) sensor is one of the most applications. The essay will discuss the advantage foe FBG sensor that other sensors are hard to achieve. In mechanical measurement field, FBG sensor most applies on uniform strain field or specific point measurement by measuring FBG sensor’s reflect peak wavelength. This essay is using FBG sensor to measure the linear strain gradient by calculating the area of reflected spectrum, and the results are highly consistent with the simulation of coupled-mode theory. Through power meter, we can obtain the spectrums’ area size without post processing to measure the variance of strain gradient immediately. Since FBG sensors are thin (in diameter) and flexible, we utilize it to measure the string structure with even smaller diameter than FBG sensor which is hard to be measured by other contact sensor. The result shows that FBG sensor not only can measure thin string structure but also has high sensitivity of small strain variance by power modulated sensing system. We extend FBG sensor’s application to measure shape-memory alloy (SMA) with collocation, since SMA’s self-sensing model is hard to build and the accuracy is easy to effect by environment