# Optical Fiber Current Sensors Based on FBG and Magnetotstrictive Composite Materials
## 3 Optical Fiber Current Sensor Based on Magnetostirctive Composite Materials
### Magnetstrictive Composites
The relationship between magnetostriction and magnetic field strength of composites with and without magnetic field heat treatment was studied. It is found that the magnetostriction of the composites after magnetic field heat treatment is greater than that of the composites without magnetic field heat treatment. At the same time, the authors compare the magnetostriction of composite materials under the pre-compression stress of 0 MPa, 2 MPa, 4 MPa, and 6 MPa, respectively. The results show that the magnetostriction of the composite material is maximum when the pre-compression stress is 6 MPa and minimum when the pre-compression stress is 0 MPa, regardless of whether the composite material is heat-treated by magnetic field. The strain model of magnetostrictive composites was put forward by [PERSON] et al. [37] The experimental results show that the theoretical model is close to the experimental results. In this paper, the properties of composites with pre-compression stress of 14 MPa and 7 MPa were studied. It is found that the magnetostriction of the composite material is greater when the pre-compression stress is 14 MPa than when the pre-compression stress is 7 MPa. At the same time, the author believes that the saturation magnetostriction of composites increases with the increase of particle volume fraction at low particle volume fraction; However, when the particle volume fraction is greater than 85%, the saturation magnetostriction of the composite decreases with the increase of particle volume fraction. [PERSON] et al. [38] studied the effects of segment soft-hard ratio, particle size, particle mass fraction, and orientation magnetic field on magnetostrictive composites. When the particle size and mass fraction are the same, the magnetostriction of the composites is the highest when the ratio of segment hardness to segment hardness is 1.5. When the weight fraction of particles is 30%, the magnetostriction of composites with particle sizes ranging from 0-38 \(\upmu\)m, 106-212 \(\upmu\)m, 212-300 \(\upmu\)m and 0-300 \(\upmu\)m is compared. It can be found that when the particle size ranges from 212 \(\upmu\)m to 300 \(\upmu\)m, the magnetostriction of the composites is the highest. Under the same ratio of soft to hard segments, when the weight fraction of particles is 70%, the magnetostriction of the composites is maximum. At the same time, the author compares the properties of the composites when the magnetic field orientation is 0\({}^{\circ}\), 40\({}^{\circ}\), 60\({}^{\circ}\)and 90\({}^{\circ}\), and finds that the magnetostriction of the composites is the largest when the magnetic field orientation is 90\({}^{\circ}\). [PERSON] et al. [39; 40; 41] studied the effects of particle mass fraction, preloading stress, particle size, orientation magnetic field, and surface treatment on magnetostrictive composites. When the pre-compression stress is 0 MPa and 1 MPa respectively, the magnetostriction of composites with pre-compression stress of 1 MPa is greater than that of composites with pre-compression stress of 0 MPa. The author compared the relationship between magnetostriction and magnetic field strength of composites with alloy particle mass fraction of 84%, 87%, 90%, 93% and 96%. When the mass fraction of particles is 93%, the magnetostriction of the composites is maximum. TD particles are classified into four grades: 0-80 \(\upmu\)m, 80-200 \(\upmu\)m, 200-450 \(\upmu\)m and 450-900 \(\upmu\)m, among which the maximum magnetostriction coefficient of composites is obtained when the particle size is 450-900 \(\upmu\)m.  
At the same time, the author found that the properties of the composite material were further improved after applying orientation magnetic field and particle surface treatment. [PERSON] et al. (2019) studied the influence of particle size on magnetostrictive composites.