# Optical Fiber Current Sensors Based on FBG and Magnetotstrictive Composite Materials
## 3 Optical Fiber Current Sensor Based on Magnetostirctive Composite Materials
### Magnetstrictive Composites
At the same time, the composite samples were prepared at the curing temperatures of 15 \({}^{\circ}\)C, 40 \({}^{\circ}\)C, 60 \({}^{\circ}\)C and 80 \({}^{\circ}\)C, respectively. When the curing temperature was 80 \({}^{\circ}\)C, the magnetostriction of the composite was the highest. [PERSON] et al. [48] studied the effects of particle size and molding pressure on the properties of magnetostrictive composites. The author classified the particle size into 38-58 \(\upmu\)m, 58-104 \(\upmu\)m, 104-150 \(\upmu\)m, 150-250 \(\upmu\)m and 250-420 \(\upmu\)m. It is found that among the five grades of particle sizes, when the particle size is 250-420 \(\upmu\)m, the magnetostriction of the composites is the largest. At the same time, when the forming pressure is 200 MPa, 400 MPa, 600 MPa, 800 MPa, and 1000 MPa respectively, the magnetostrictive strain of the composites with the forming pressure of 400 MPa is the maximum. The author thinks that the molding pressure reduces the voids in the material, increases the density of the composite, and then improves the properties of the composite. [PERSON] et al. [49] studied the effect of powder crystal orientation on the properties of magnetostrictive composites. It is found that the magnetostriction of 0-3 type or 1-3 type composites presents different trends. When the crystal orientation is \(<\) 110 \(>\), the magnetostrictive strain of type 1-3 composites is greater than that of type 0-3 composites. When the crystal orientation is \(<\) 100 \(>\), the magnetostrictive strain of type 0-3 composites is greater than that of type 1-3 composites. However, under the same externally applied magnetic field, the magnetostrictive strain of 1-3 type composites with crystal orientation \(<\)110 \(>\) is greater than that of 0-3 type composites with crystal orientation \(<\)100\(>\). [PERSON] et al. [50] studied the effects of orientation magnetic field and preloading stress on magnetostrictive composites. The grain size of magnetostrictive powder used is 200-300 \(\upmu\)m. Magnetostrictive composites were cured in oriented magnetic fields with magnetic field strengths of 0 Oe, 4000 Oe, 8000 Oe and 12,000 Oe, respectively. Converted to the international system of units, 1 Oe is equal to 1000/4\(\uppi\) (\(\approx\)79.5774715) A/m. It is found that when the magnetic field intensity of the orientation magnetic field is 8000 Oe, the magnetostrictive strain of the composite material is the largest. At the same time, when the magnetic field intensity of the orientation magnetic field is 8000 Oe, the author applies pre-stress of 0 MPa, 5 MPa, 9 MPa, 13 MPa, and 17 MPa to the composite material. Among them, the magnetostrictive strain of the composites is the largest when the pre-compression stress is 17 MPa. Compared with the pre-compression stress of 0 MPa, the magnetostriction of the composite should be about doubled when the pre-compression stress is 17 MPa. [PERSON] et al. [51] studied the influence of magnetostrictive materials on the properties of composites. The author compared the relationship between the magnetostriction of TbDyHoFe alloy, TbDyHoFe composite material and TbDyFe composite material and the applied magnetic field. The magnetostriction of TbDyFe composite material reaches saturation at 400 kA/m, and the magnetostriction of TbDyHoFe alloy and TbDyHoFe composite material reaches saturation at 250 kA/m. In addition, the saturation magnetostriction of  
Figure 20: Relationship between saturation magnetostriction and particle aspect ratio of composites with different particle volume fractions. the TbDyFe composite material is the largest, and the saturation magnetostriction of the TbDyHoFe alloy is the smallest. In the low magnetic field (<100 kA/m), the magnetostriction of the TbDyHoFe composite is the largest, i.e., the sensitivity of the TbDyHoFe composite is higher under the low magnetic field. [PERSON] et al. [52] studied the influence of the intensity of the orientation magnetic field on the properties of magnetostrictive composites.