| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 96 === Recently, the optical fiber sensing technologies, especially fiber Bragg grating (FBG) sensors, have been rapidly developed due to the advantages such as excellent mechanical properties, high sensitivity and electromagnetic immunity. The measurement ability of FBG sensors in static and low frequency responses has been demonstrated, and there are many successful engineering applications. However, further investigations are needed for FBG to improve the measurement ability in high frequency and transient responses.
In the theoretical analysis of FBG, the coupled-mode theory is used to present the reflected spectra and to simulate the responses under static and dynamic strain fields. The results indicate that the sensitivity declines with the increase of input frequency and the increase of frequency and amplitude of strain result in signal distortion. The concept of distortion that limit the practical applications is established to discuss the dynamic sensing range of FBG.
In the experiments of FBG, the power modulated sensing system is established to measure the transient responses of dynamic strain for structural components under impact loadings, which include solid rod, hollow tube and suspended cable. The strain gage is also used to measure simultaneously with the FBG sensors to compare the results obtained from two different techniques. In addition, the frequency spectra of experimental results are analyzed and compared with theory and finite element method. According to the available results, it is proved that FBG sensors have excellent ability for dynamic strain measurement. At the same time, the transient wave propagation properties of structural components are analyzed in detail and the associated applications are established.
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