Title page for ETD etd-11198-54532


Type of Document Dissertation
Author Oh, Ki Dong
Author's Email Address okd@ee.vt.edu
URN etd-11198-54532
Title Optical Fiber Fabry-Perot Interferometer based Sensor Instrumentation System for Low Magnetic Field Measurement
Degree PhD
Department Electrical and Computer Engineering
Advisory Committee
Advisor Name Title
Wang, Anbo Committee Chair
Besieris, Ioannis M. Committee Member
Claus, Richard O. Committee Member
Lin, Tao Committee Member
Murphy, Kent A. Committee Member
Keywords
  • Fabry-Perot Interferometer
  • Magnetic Field Sensor
  • Temperature Compensation
  • Optical Fiber
Date of Defense 1997-12-18
Availability unrestricted
Abstract
This dissertation proposes a miniaturized optical fiber based sensor system for the measurement of 3-dimensional 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 depends on the magnetic fields applied to the sensor. Since the diameter of the magnetostrictive sensor gage is 125 micrometer which 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/out fiber, and a passive temperature compensator. In addition, it also enhances the mechanical strength and compactness of the sensor. This sensor design shows 98 percent suppression of the thermally induced sensor output changes. The linear output of the sensor system is enhanced by transverse field annealing which increases magnetostrictive induction in the ferromagnetic sensor gage material and controls the sensor gage geometry. 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 percent of fringe visibility, which further improves the performance of the interferometer. The signal fading in the interferometric sensors at the peak or bottom of a fringe is reduced by using a quadrature signal demodulation method. The system has been shown to have a resolution better than 100 nT over a measurement range from 100 to 40,000 nT. This research is supported financially by the Phillips Laboratory of the U.S. Air Force.
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