An improved fiber sensor consisting of a fiber Bragg grating (FBG) and an extrinsic Fabry-Perot interferometric (EFPI) sensor is proposed. The interferometric cavity of the improved sensor is composed of a glass capillary tube and two sections of single-mode fiber (SMF), the segment near one of the SMF’s end faces has a FBG. One of the two aligned SMFs is free along the axial direction in the testing specimen, which is different from the traditional structure. During the cryogenic test, only the glass tube and the free SMF with a FBG which exposed outside the glass tube part will be encapsulated by cryogenic adhesives on the testing oxygen-free copper specimen. The temperature and strain performance of the testing oxygen-free copper specimen were studied at high vacuums and low temperatures range 273 K to 30 K. The testing result was agreed well with the theoretical values. The improved sensor is compact, easy in fabrication and has high potentials in cryogenic temperature applications.
Traditional electrical sensor or traditional fiber Bragg grating sensing technology is not applicable to the measurement of nonuniform strain in composite material. Therefore, the distributed nonuniform strain in the lap plate position of composite interlining material is measured using a single fiber with optical frequency domain reflection technology in this study. The experimental results show consistency with the experiment phenomena, and the measurement accuracy could be increased to the submillimeter level.
Because of the high degree of railway’s electromagnetic radiation and the vulnerability of the traditional electronic sensor, the safety monitoring of railway’s protective net in slopes is an important process. Based on fiber grating’s such advantages as freedom from electromagnet, and the convenient linkage of signal, this thesis formulated tension sensor and acceleration sensor on the basis of protective net’s characteristics. By conducting the impulse test on the protective net that is installed with sensor, we collected the mechanics’ parametric variation during the whole process of impact. The fiber grating sensor used in the test was stable and reliable.
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