# Optical Fiber Current Sensors Based on FBG and Magnetotstrictive Composite Materials
## 3 Optical Fiber Current Sensor Based on Magnetostirctive Composite Materials
### Sensor Structure
[17] proposed an optical fiber current sensor based on low-quality magnetostrictive materials, as shown in Figure 11. The cost of the proposed sensor is further reduced, and only 2.0 g of Terfenol-D alloy is used. The finite element  
Figure 10: Ring optical fiber current sensor based on 5.6 g magnetostrictive material. Figure 9: Optical fiber current sensor based on 70 g rectangular magnetostrictive material. simulation shows that the magnetic flux density of FBG attached to the fiber-optic current sensor based on 2.0 g magnetostrictive material is significantly increased compared with the fiber-optic current sensor based on 5.6 g magnetostrictive material. The sensitivity of the optical fiber current sensor based on 2.0 g magnetostrictive material is twice that of the optical fiber current sensor based on 5.6 g magnetostrictive material, and the measurement error of both is less than 3%. Transient response test shows that there is no obvious delay between the input and output signals of the sensor, which indicates that the sensor is suitable for fault detection. [PERSON] et al. [18] proposed an optical fiber current sensor based on hyperboloid magnetostrictive composite material, and the proposed that the sensor only uses 1.5 g of Terfenol-D alloy. The sensor adopts an open-loop structure, which can not only reduce the use of magnetically permeable materials, but also allow convenient installation of the sensor. TD alloy is the main magnetostrictive material. Because TD alloy is expensive, fragile and difficult to form, magnetostrictive composite material is used instead of magnetostrictive material. Magnetostrictive composite material is composed of TD alloy powder and epoxy resin. FBG embedded in magnetostrictive composite allows the sensor to have a frequency response of 60 kHz. As shown in Figure 12, the shape of magnetostrictive composite is hyperboloid, which not only reduces the use of TD alloy, but also improves the sensitivity of the sensor. When the input signal produces a current step of 150 A, the response time of the sensor is only 1.5 ms. The sensor based on hyperboloid magnetostrictive composite material not only reduces the production cost and improves the sensitivity of the sensor, but also reduces the response time of the sensor. [PERSON] et al. [19] proposed an optical fiber current sensor with concentrated magnetic flux density based on magnetostrictive composite material, and the mass of Terfenol-D alloy used in the proposed sensor was only 0.42 g. The author uses FEM to optimize the geometry of the optical fiber current sensor. As shown in Figure 13, the structure of the magnetically permeable material is arranged in a ring structure from thick to thin, which not only reduces the usage amount of the magnetically permeable material, but also makes the magnetic flux density on the magnetic field telescopic composite material more concentrated. The author studied the number of different permanent magnets and found that when the number of permanent magnets is 5, the maximum non-linear error of the sensor is only 0.15%. The proposed sensor not only reduces the production cost and improves the sensitivity, but also reduces the maximum non-linear error of the sensor. As shown in Table 1, several kinds of current sensors based on FBG for high-voltage lines are compared in this paper. Figure 5:0 Ring optical fiber current sensor based on 2.0 g magnetostrictive material. [PERSON] et al. [20] proposed a fiber grating current sensor with enhanced sensitivity based on giant magnetostrictive material. When subjected to preloading stress, GMM sensitivity to magnetic field increases significantly. According to this characteristic, the beam is added to the conventional rectangular GMM to bear the applied pressure, thus forming a T-shaped structure, as shown in Figure 5:1 The material of the beam is 304 stainless-steel. A T-shaped structure is placed in a copper support structure.