# Optical Fiber Current Sensors Based on FBG and Magnetotstrictive Composite Materials
## 3 Optical Fiber Current Sensor Based on Magnetostirctive Composite Materials
### Magnetstrictive Composites  
The performance of magnetostrictive composites directly affects the performance of sensors, so it is necessary to study magnetostrictive composites. There are two main preparation methods of magnetostrictive composites, namely powder sintering method and powder bonding method. Powder sintering method refers to grinding magnetostrictive \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Serial** & **Author** & **Architectural Feature** & **Advantages and Disadvantages** \\ \hline
**1** & [PERSON] [13] & \
\begin{tabular}{c} 1.40 g cylindrical rod magnetostrictive material \\ 2. preloading stress mechanical device \\ 3. DC bias coil \\ \end{tabular} &
\begin{tabular}{c} The linearity of the sensor is high, but the structure is complex and the sensor is active. \\ \end{tabular} \\ \hline
**2** & [PERSON] [14] & \
\begin{tabular}{c} 1.144 g annular solid magnetostrictive material \\ 2. stainless-steel compression ring \\ \end{tabular} &
\begin{tabular}{c} The measurement of alternating current is \\ realized with small measurement error, but the \\ frequency-doubling phenomenon \\ will occur in the measurement process. \\ \end{tabular} \\ \hline
**3** & [PERSON] and [PERSON] [15] & \
\begin{tabular}{c} 1.74 g solid cuboid magnetostrictive material \\ 2. permanent magnet \\ \end{tabular} &
\begin{tabular}{c} The sensor is passive and eliminates the \\ phenomenon of frequency-doubling, \\ but magnetostrictive materials are expensive \\ and fragile. \\ \end{tabular} \\ \hline
**4** & [PERSON] [16] & \
\begin{tabular}{c} 1.5.6 g annular magnetostrictive material \\ 2. annular magnetic conductive material \\ \end{tabular} &
\begin{tabular}{c} The cost of the sensor is greatly reduced, and the \\ sensitivity is high, but the magnetostrictive \\ material is difficult to form. \\ \end{tabular} \\ \hline
**5** & [PERSON] [17] & \
\begin{tabular}{c} 1.2.0 g annular magnetostrictive material \\ \end{tabular} &
\begin{tabular}{c} Further reduce the cost and improve the \\ sensitivity, which is suitable for \\ fault detection. \\ \end{tabular} \\ \hline
**6** & [PERSON] [18] & \
\begin{tabular}{c} 1.15 g hyperboloid magnetostrictive material \\ 2. open-loop structure \\ \end{tabular} &
\begin{tabular}{c} Lower cost, higher sensitivity, faster response \\ time, and easy installation. \\ \end{tabular} \\ \hline
**7** & [PERSON] [19] & \
\begin{tabular}{c} 1.042 g rectangular magnetostriction material \\ 2. circular magnetic permeability material \\ from coarse to fine \\ \end{tabular} &
\begin{tabular}{c} The cost is the lowest, the magnetic flux density \\ is concentrated and the maximum non-linear \\ error of the sensor is reduced, but the \\ temperature error is not compensated. \\ \end{tabular} \\ \hline
**8** & [PERSON] [20] & \
\begin{tabular}{c} 1. The T-shaped structure is placed in the \\ copper support structure \\ 2. the copper screw exerts pressure \\ \end{tabular} &
\begin{tabular}{c} Sensitivity is enhanced, \\ but the structure is complex. \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Research summary of sensor structure. Figure 14: Optical fiber current sensor based on magnetostrictive material with enhanced sensitivity. alloy into powder under a vacuum or under the protection of rare gas, pressing and molding in a mold after drying, and finally sintering under the protection of inert gas [21; 22]. The bonding method breaks the magnetostrictive alloy into powder by a proper method, then mixes the powder with the selected binder evenly in proportion, pressing, extruding or injecting in a magnetic field and finally solidifying at a specific temperature [23]. [PERSON] et al. [24] studied the effects of orientation magnetic field and pre-compression stress on magnetostrictive composites.