Application of Magnetostictive Composite in an Electric Current Sensor Application of Magnetostictive Composite in an Electric Current Sensor Suha Lasassmeh and Brett Sweeney Department of Electrical Engineering, University of Wisconsin-Milwaukee Advisors: Dr. Chiu Law, Dr. Rani El-Hajjar 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 (See Fig 1), it is ideal for current sensing. Fiber Bragg gratings (FBG) are passive devices that are mainly used as optical filters in a communication network for multiplexing or demultiplexing optical signals. Main parameters to consider in a FBG is its reflection wavelength (Bragg wavelength λ B ), the effective refractive index of a fiber (n eff ), and the grating period (Λ) as shown in Fig 2. Coupling T-D with a FBG forms a sensor that is compact, lightweight, immune from electromagnetic interference. Fig 1. Fig 1. The behavior of Terfenol-D with the application of magnetic field. Fig 2 Fig 2. FBG

Sensor Structure The FBG is epoxied between two identical composites in rectangular shape with triangular distribution of Terfenol-D particles. This produce an approximately linear strain distribution along the FBG. As a result, the optical signal reflected by the FBG has a spectral width proportional to the magnetic field. 3D printer was used to make the required molds for sensor prototyping. Strain gauges where used to measure the strain before embedding the FBG. Fig 3. Fig 3. Experiment setup and sensor prototyping

Modeling the Sensor and the Resutls Energy based model used to describe the magnetostrictive behavior of Terfenol-D. Magnetization orientations for the cubic TbDyFe alloy determined by the local minima of the total free magnetic energy. Fig 5 Fig 5. Three dimensional energy surface with H=0. Fig 6 Fig 6. Three-dimensional energy surface with H=10kA/m. Fig 9. Fig 9. 3D view of the sensor geometry. Fig 10. Fig 10. Surface plot of stress component. Fig 7 Fig 7.Displacement at Large End Fig 8 Fig 8. Displacement at Small End Where E K, E field, are the magnetocrystalline anisotropy energy and the external magnetic field energy respectively. α i denotes the direction cosine of the magnetization with respect to the crystal axes,, and and K 0, K 1, K 2 are the zero-order, first-order and second-order magnetocrystalline anisotropy constants respectively. H denotes the magnetic field, β i and is the direction cosine of the magnetic field with respect to the crystal axes. M s is denoted as the saturation magnetization and μ 0 is the magnetic permeability coefficient of free space. Table 1: Properties of Terfenol-D. Fig 4 Fig 4. Cubic crystal orientation of Terfenol-D.