DESIGN OF FIBER OPTICAL CURRENT SENSOR David Matthew Frailey, Electrical Engineering and Computer Science Dr. Chiu Law, Electrical Engineering and Computer Science Dr. Rani Elhajjar, Civil/Environmental Engineering, Materials Science

DESIGN OF FIBER OPTICAL CURRENT SENSOR Objectives and Approach Analyze the physical factors determining the performance of a fiber optic magnetic field sensor based on a magnetostrictive composite and compare with experimental results. Tailor the frequency chirping of the fiber Bragg grating which enables appropriate sensor responses By using a Terfenol-D/epoxy composite, unique geometries can be easily manufactured. Large particles of Terfenol-D (100-300microns) were mixed with epoxy and then aligned in an external magnetic field which show a magnetostriction coefficient similar to bulk material Terfenol-D.

DESIGN OF FIBER OPTICAL CURRENT SENSOR Theory From theoretical calculations which were verified by COMSOL, the magnetization of each sample can be acquired. The first sample had the 3cm FBG was embedded in the middle of the sample and for the second sample, the 3cm FBG was placed towards the base. This was to ensure a linear approximation of the magnetization. The strain is proportional to the internal magnetization squared. This allows to find the grating length of the FBG as a function of magnetization. By knowing the grating length as a function of magnetization, the optical properties of the FBG under different magnetic fields can be known.

DESIGN OF FIBER OPTICAL CURRENT SENSOR Theoretical and Experimental Results Reflected Spectrum Reflected Optical Power Reflected Spectrum Reflected Optical Power Sample 1: Trapezoidal Prism Sample 2: Concave Trapezoidal Prism

DESIGN OF FIBER OPTICAL CURRENT SENSOR Applications By measuring either the central wavelength, the reflected optical power, or both, the external magnetic field can be acquired. For cost reasons, the reflected optical power would be cheaper since only a basic circuit schematic is needed. Sensitivity of the sensor is tunable by the geometry of the sample which allows for a wide range of applications. Terfenol-D/Epoxy composites show little hysteresis under alternating magnetic fields up to 20 KHz. This allows for both AC and DC applications for the sensor such as leaky transmission lines, heavy duty power equipment such as DC cranes, and EMC standard tests.