Miniaturized Optical Fiber Magnetic Field Sensors for On-Board Environmental Diagnostics
Final rept. 15 Aug 95-30 Dec 97
VIRGINIA POLYTECHNIC INST AND STATE UNIV BLACKSBURG FIBER ELECTRO-OPTICS RESEARCH CENTER
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A miniaturized optical fiber based sensor system has been developed for the measurement of vector magnetic fields. The operation of the sensor system is based on the detection of magnetostrictive dimensional changes in the sensor gage using a modified extrinsic Fabry Perot Interferometer configuration. Because of the magnetostrictive reflector the gap length of the Fabry Perot cavity formed by the two fiber ends depends on the magnetic fields applied to the sensor. Since the diameter of the magnetostrictive sensor gage is the same as that of the input output fiber, the sensor is simply constructed by inserting the sensor gage and the input output fiber into a small glass tube. The glass tube serves as both an aligner for the sensor gage and input output fiber, and a passive temperature compensator. This sensor design shows 98 suppression of the thermally induced sensor output changes. A 5 times increase in sensor sensitivity is obtained with the transverse field annealing and the use of a new magnetostrictive material. A modified sensor gage endface demonstrates 92 of fringe visibility, which further proves the performance of the interferometer. The system has been shown to have a resolution better than 100 nT over a measurement range from 100 to 40,000 nT.
- Fiber Optics and Integrated Optics