# Optical Fiber Current Sensors Based on FBG and Magnetotstrictive Composite Materials
## 3 Optical Fiber Current Sensor Based on Magnetostirctive Composite Materials
### Magnetstrictive Composites
Magnetostrictive composites with the same particle volume fraction were prepared by using five narrow distribution particles (30-53 \(\upmu\)m, 53-150 \(\upmu\)m, 150-300 \(\upmu\)m, 300-450 \(\upmu\)m, 450-500 \(\upmu\)m) and one wide distribution particle (30-500 \(\upmu\)m). The adopted binder is unsaturated polyester resin. The experimental results show that among the five narrow distribution particles, the composite with particle size of 53-150 \(\upmu\)m has the highest magnetostriction. However, the magnetostriction of composite materials prepared with wide distribution particles (30-500 \(\upmu\)m) is greater than that of all composite materials prepared with narrow distribution particles. As far as the average particle size is concerned, it can be seen from the comparison of five kinds of narrow particle composites that the saturation magnetostriction coefficient first increases and then decreases with the increase of the average particle size, and reaches the maximum when the average particle size is 102 \(\upmu\)m (particle size distribution is 53-150 \(\upmu\)m). [PERSON] et al. (2019) studied the influence of bonding process on the properties of magnetostrictive composites. In this paper, the alloy powders are classified into four different sizes: 0\(\sim\)100 \(\upmu\)m, 100-150 \(\upmu\)m, 150-300 \(\upmu\)m and 300-350 \(\upmu\)m. When the applied magnetic field is 13 kOe and the molding pressure is 100 MPa, the saturation magnetostriction of the composite material is maximum when the particle size is 100-150 \(\upmu\)m. At the same time, it is found that the magnetostriction of composites increases with the increase of molding pressure. When the molding pressure is 150 MPa, the magnetostriction reaches the maximum value, and then decreases with the increase of molding pressure. This shows that when the molding pressure is 150 MPa, the alloy particles and binder in the composite have been closely bonded, but with the continuous increase of molding pressure, the magnetostriction decreases gradually, because the higher molding pressure will hinder the fluidity of particles in the sample, thus affecting the magnetostriction performance of the sample. [PERSON] et al. (2019) studied the influence of milling and other processes on the properties of magnetostrictive composites. In this paper, the author adopted the milling process of disc milling and ball milling, and prepared the alloy powder obtained by the two milling processes into composite materials. The results show that the magnetostrictive properties of the composites prepared by ball milling and disk milling have little difference. Therefore, the milling process adopted in this experiment has little effect on magnetostrictive properties. [PERSON] et al. (2019); [PERSON] et al. (2020); [PERSON] et al. (2020) studied the effects of preparation technology, particle volume fraction, particle length-width ratio, and curing temperature on the properties of magnetostrictive composites. In the preparation process of composite materials, the author treated the mixture of magnetostrictive particles and resin by mechanical stirring and high-energy ultrasonic, respectively. It is found that the magnetostriction of composites treated by high-energy ultrasonic method is greater than that of composites treated by mechanical stirring method. This is because the high-energy ultrasonic method can not only disperse the particles evenly, but also remove the oxidation on the surface of the particles. As shown in Figure 20, when the aspect ratio of particles is the same, the saturation magnetostriction of composites with 50% particle volume fraction is greater than that of composites with 20% and 30% particle volume fraction. When the particle content is the same, the saturation magnetostrictive strain of magnetostrictive composites increases with the increase of particle aspect ratio. However, when the aspect ratio of the composite is greater than 10, the saturation magnetostriction of the composite has little change with the aspect ratio of the composite.