Magnetostriction-Based Fiber Optical Current Sensors by  Suha Lasassmeh and Edward Lynch Advisor: Prof. Chiu Law 

Introduction A novel fiber optical current sensor (FOCS) based on a giant magnetostrictive material, Terfenol-D (T-D), is investigated. T-D expands and contracts under magnetic fields, it is ideal for current sensing . Fiber Bragg gratings (FBGs) are passive devices that are mainly used as optical filters in a communication network for multiplexing or demultiplexing optical signals. 2

Sensor design and modeling Magnetostrictive composite structure manufactured using a blend of epoxy and 106- 300 μm T-D particles in random orientation. Magnetostrictive strain of the composite structure measured experimentally with digital image correlation by painting it with a speckle pattern and FOCS (FBG embedded into the structure) response measured with a wavelength. Magnetic field and magnetostrictive strain modeled by COMSOL and FOCS response simulated by Matlab based on monolithic T-D structure with the same geometries as those of the composite structure but markedly better magnetic properties. 3

Results Fig 7. Simulated FBG Total Power Response 4 Comsol Model – T-D Epoxy FBG OCS. Strain along Z axis, H = 10 [kA/m]. Simulated Strain Along FBG. Experimental FBG Spectral Power Response. 4 Fig 7. Simulated FBG Total Power Response

Conclusion The T-D /epoxy composite will overcome the drawbacks (e.g. fragility and thermal drift) of other FOCS that utilize monolithic T-D. The cone shaped composite structure creates a field gradient. The original grating period of the FBG embedded in the magnetostrictive composite becomes aperiodic when it is strained by the field gradient under external H and widens its spectrum. Future topics include testing FBG bonding and thermal variations.