# 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 particle mass fraction of 85%, 90% and 93% were prepared by the authors, and the maximum magnetostriction of the composites was obtained when the particle mass fraction was 90%. This is because when the mass fraction of particles is low, the distance between TD particles is large, and the resin hinders the transmission of magnetostriction; When the mass fraction of particles is high, TD particles are prone to cluster phenomenon; Therefore, the overall magnetostriction of the composite material is small. Then, the author sifted TD particles into 0-74 \(\upmu\)m, 74-150 \(\upmu\)m and 150-300 \(\upmu\)m. It is found that GMPC has good magnetostrictive properties when the particle size is 74-150 \(\upmu\)m and 150-300 \(\upmu\)m. This is because fine alloy particles have large specific surface area and are easy to oxidize, which is not conducive to the properties of composite materials. At the same time, the author compares the relationship between magnetostriction and magnetic field strength of GMPC at molding pressures of 200 MPa, 300 MPa, and 450 MPa, respectively. However, with the increase of molding pressure, the magnetostriction of GMPC increases only slightly. This shows that when the molding pressure is 200 MPa, the compact bonding between alloy particles and binder is basically realized. [PERSON] et al. [34] compared the effects of orientation magnetic field and particle volume fraction on magnetostrictive composites during curing, as shown in Figure 19. First, TD particles and epoxy resin were mixed evenly in a mold, then degassed in vacuum for 30 min, and finally, the mold was placed in air for curing. The composite material obtained was called 0-3 magnetostrictive composite material. When the mold is solidified in a magnetic field, the composite material obtained is called 1-3 magnetostrictive composite material. When the particle volume fraction is the same, the magnetostriction of type 1-3 composites is greater than that of type 0-3 composites, and the saturation magnetostriction of type 1-3 composites reaches 72% of TD alloy. At the same time, the author studied the effect of particle volume fraction on composites. When the volume fraction of particles is 30%, the saturation magnetostriction of the composites is maximum. This is because when the particle volume fraction is low, the magnetostriction of the composite material is small due to the dilution effect of epoxy resin; when the volume fraction of particles is high, the magnetostriction of composites decreases due to the poor contact between particles. Figure 19: (**a**) Effect of orientation magnetic field on magnetostrictive composites during curing. (**b**) Effect of particle volume fraction on magnetostrictive composites during curing. [PERSON] et al. [35] studied the effects of particle volume fraction and temperature on the properties of composites. At room temperature, the author selected Spurr low viscosity epoxy resin as binder, and tested magnetostrictive composites with particle volume fractions of 13%, 23%, 31%, 37% and 50%, respectively. It is found that when the particle volume fraction is 50%, the saturation magnetostriction of the composites is maximum. At the same time, with the same volume fraction of particles, the author studied the effect of temperature on the saturation magnetostriction of composites. When the temperature is 0 \({}^{\circ}\)C or 10 \({}^{\circ}\)C, the saturation magnetostriction of magnetostrictive composites reaches the maximum. At present, the research aims of most literature are 0-3 magnetostrictive composites and 1-3 magnetostrictive composites. [PERSON] et al. [36] proposed 2-2 magnetostrictive composites, i.e., the mixture of TD particles and epoxy resin was annealed for 15 min under a magnetic field of 240 kA/m under vacuum. The mixture was then cooled to room temperature under a magnetic field. The obtained sample is 2-2 magnetostrictive composite material.