Application of Strain and Magnetic Sensing based on the Comb-type Long-period Fiber Grating

• Main Authors: Wang, SHENG-FENG, 王聖丰
• Other Authors: CHIANG, CHIA-CHIN
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/fn284a

博士 === 國立高雄應用科技大學 === 機械與精密工程研究所 === 104 === In this paper, we utilize lithography technique along with etched optical fibers and SU-8 3050 photoresist to product long-period fiber grating (LPFG). The periodic comb-type structure of photoresist is patterned onto the LPFG. Then, we adopt the PDMS, which is a kind of polymeric organosilicon compound, to coat the grating structure of LPFG, and the packaged comb-type LPFG (PCLPFG) is fabricated. Subsequently, we use the electroforming process to deposit the nickel within the patterned periodic structure and we will obtain the metallic comb-type LPFG (MCLPFG). First, we use the PCLPFG sensors to detect the variations of the longitudinal and transverse loading. According to the results of the experiments, we can find that when the longitudinal and transverse loading are strengthen, the phenomenon of the transmission loss agrees with the coupled-mode theory and the dips of transmission loss perform as a quadratic function of cosine. We also execute the experiment of the axial loading test for three times to ensure the feasibility and reproducibility of the proposed optical fiber grating sensors. The better sensitivities of sensors are -53.892 dB/N and 0.00946dB/με, and the corresponding period of the fiber gratings are 600 and 620 μm. During the process of the magnetic field sensing experiment, we use the MCLPFG sensors to detect the strength of external applied magnetic field. In order to avoid thermal effect, we employ the NdFeB magnet to generate the magnetic field. The strength of magnetic flux density is determined by adjusting the vertical distance between the NdFeB magnet and metallic grating structure of MCLPFG. We also use the Gaussmeter to execute the real-time probing of the magnetic flux density. According to the results of the experiments, we can find that when the magnetic flux density is strengthen, the magnetic force would attract the metallic grating structure and induce the variation of strain induced refractive index. The phenomenon of the transmission loss agrees with the coupled-mode theory and the dips of transmission loss would descend or ascend. The best sensitivity is 0.04528 dB/Gauss at the grating period of 630 μm.