Magnetic Fiber Sensor By Using Air-Gap Long Period Grating

• Main Authors: Hung-Yu ChangJian, 張簡鴻宇
• Other Authors: Wen-Fung Liu
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/37610898719603333051

碩士 === 逢甲大學 === 電機工程所 === 98 === The content of this thesis proposes the magnetic sensor based on an air-gap long period fiber grating (AG-LPG). This sensing device is composed of an AG-LPG fabricated by the semiconductor manufacturing process and surrounded with a smart materials-magnetic fluid. The AG-LPG is fabricated by combining the fiber side-polishing, fiber lithography and fiber etching method to produce the periodic air-gap grating in the core along the fiber axis of single mode fibers. Then, the grating region is immersed in the magnetic fluid and then packaged for achieving the magnetic sensor. The change of the surrounding refraction index (SRI) by magnetic field and the grating period will affect the resonant peak shift as well. For the measurement of forward DC magnetic field, the maximum shift of resonant wavelength of 14.4 nm in the field range from 3.3 to 114.8 Gauss is experimentally demonstrated with the sensitivity of about 0.12737nm / Gauss. For measuring the backward magnetic field, the experimental results demonstrated that the shift of resonant wavelength of 9 nm is obtained in the field range from -114.8 to -3.3 Gauss, which corresponds to the sensitivity of about -0.06778nm / Gauss. For the measurement of AC magnetic field, the frequency increment in the constant voltage will reduce the number of magnetic chains and then to decrease the refractive index of magnetic fluid materials, which will cause the wavelength shift toward the shorter-wavelength side. However, with increasing magnetic field-magnitude in a constant frequency, the index of magnetic fluid will increase due to the number increment of lead flux and then to cause the grating wavelength shift toward the longer-wavelength side. The novel magnetic fiber sensor can be applied in the measurement magnetic filed of dangerous or special environment.