聚偏二氟乙烯薄膜與布拉格光纖光柵感測器之動態量測技術研發與應用

Abstract

本研究主要著重於開發聚偏二氟乙烯(PVDF)壓電薄膜與布拉格光纖光柵(FBG)感測器的動態量測技術。關於懸臂樑的暫態行為部分，利用PVDF具有高靈敏度與可量測壓力的特性，取得外力撞擊結構物的波源歷時過程，並帶入理論計算與有限元素模擬懸臂樑的暫態應變與位移，最後將理論分析與有限元素法數值計算的暫態波傳響應結果跟實驗量測進行比較，討論Bernoulli-Euler跟Timoshenko樑理論在厚樑結構上的適用性。分析三維結構物邊線上的波傳行為一直是個難以量測的工程問題，本研究結合分波多工器(CWDM)與能量調變法解調技術，有效的抑制光電轉換器於FBG量測範圍之外的暗電流(dark current)，增加感測系統的靈敏度，成功開發出能同時進行多區段且低損耗的量測系統，大幅度提昇FBG感測器的工業應用能力，並利用光纖的幾何特性將其黏貼在結構物的邊線上進行三維應變量測，最後將FBG量測的動態應變訊號跟有限元素法數值模擬的結果進行驗證。鋰電池在充放電的過程中，堆疊在固態電解質介面(SEI)上的鋰離子，會因為擴散速度較慢而造成鋰電池產生額外的體積膨脹，長時間反覆使用後會讓石墨層出現裂縫，進而降低電池的儲電能力。本研究將改良式的FBG感測器埋入鋰電池的石墨電極層中，結合高速光纖光柵解調器，針對電池內部的應變與溫度變化進行長時間的監測，並同時將微型壓力計嵌入至電池上蓋的內側，紀錄充放電過程的內壓變化狀態，這些埋入電池內部的感測器，具有能提供評估電池荷電狀態(SOC)與電池健康狀態(SOH)準則的潛力。

This research is mainly focused on the development of dynamic measuring techniques using Polyvinylidene fluoride (PVDF) piezoelectric thin film and fiber Bragg grating (FBG) sensor. In regard to the transient behavior of cantilever beam, high sensitivity and pressure sensing ability are two key characteristics of PVDF film for acquiring force history of impact loading. After confirming the correctness of experimental boundary conditions, the impact loading history obtained from experimental measurement is used for Timoshenko and Bernoulli-Euler beam theories to investigate the transient responses. By comparing the theoretical and the finite element (FEM) simulation against measurement from corresponding experiments, this research is to discuss the ability of Timoshenko beam theory for calculating transient behavior under different slender ratios. Analyzing the wave propagation behavior on the edge of solid has been a changing problem with highly difficulty. This research propose the combination of coarse wavelength division multiplexing (CWDM) device with power modulated method to suppress dark current of photodiode and to realize multiple points dynamic measurement in high sensitivity. Based on the slender geometric characteristic of the optical fiber, FBG has great performance as a sensor for distinguishing the strain on the edge of an aluminum solid. In the perspective of dynamic behavior in time domain, three dimensional transient strains measured by pre-strengthen FBG sensors have great consistency with FEM simulation. Expansion and contraction of electrode particles during charge and discharge process causes large contact stresses, which leads to graphite electrode being fractured. An additional solid electrolyte interphase (SEI) is formed when the fractured graphite particles expose a fresh carbon surface to the electrolyte and the capacity of lithium ion battery is fading owing to the loss of available Li ion. With the combination of a high speed interrogator, advanced FBG sensors are embedded in graphite layer to deliver in-situ condition of temperature and strain. A miniature pressure sensor is arranged inside the top lid of battery to monitor the internal pressure variation in nominal usage. With these embedded sensors, the experimental results has the potential to evaluate the state of charge (SOC) and the state of health (SOH) of lithium ion battery.