## 3 Results
### The Experimental Analysis  
The magnetic field measurement platform is shown in Figure 7. The optical spectrum analyzer (AQ6370D) amplified spontaneous emission source, Gauss meter (CH-1500), and two 700-turn coils are used in the measurement platform. The programmable DC power (IT6164B) is used for power supply, and the magnetic field calibration is carried out by a Gauss meter with precision of 0.01 Gs. The coil will heat up with a long working time, which will lead to the increase in coil resistance and instability of magnetic field environment. The temperature will also affect the RI of MF, which will cause inaccurate magnetic field measurement data. Therefore, circulating coolant is used to reduce the temperature. The coolant driven by a motor pump circulates in the inner of the coil frame, and the pumped coolant is cooled by the fan and finally flows back to the power coil. During the experiment, the temperature was set at 20 \({}^{\circ}\)C.  
Figure 5: (**a**) The SMF receives transmitted light from SHDCF with the different lengths of SHDCF: (**a**) 3 cm; (**b**) 5 cm; and (c) 7 cm. Figure 6: The splicing effect diagram of MMF and SHDCF under different discharge intensity and discharge time: (**a**) 40 unit and 300 ms; (**b**) 30 unit and 400 ms; (**c**) 20 unit and 300 ms; (**d**) 30 unit and 300 ms. The prepared magnetic field sensor is placed on the magnetic field measurement platform, as shown in Figure 7. Gauss meter zeroing and pre-heat treatment for 30 min. The magnetic field strength is increased by 25 Gs every 20 min by increasing the output current of the DC power supply, and the measured data of each magnetic field strength are saved on the optical spectrum analyzer. Fourier transform of the magnetic field measurement data is carried out, as shown in Figure 8a, and a small amount of light passes through the air hole and cladding and causes high-order mode interference, according to the results of Fourier transform. The band-pass filter is used to eliminate the high-order mode interference from the air hole and cladding in magnetic field measurement data; the comparison of transmission spectrum before and after filtering is shown in Figure 8b. As shown in Figure 9a, the transmission spectrum after band-pass filtering of the sensor in the magnetic field range of 0-200 Gs is blue shifted with the increase in magnetic field intensity, and the sensitivity is \(-\)116.1 pm/Gs with a linearly fitted index of 0.9940, as shown in Figure 9b. The magnetic field measurement data are saved every 30 min at the magnetic field of 0 Gs for the verification of sensor stability, as shown in Figure 10. The maximum wavelength shift is 0.12 nm within 120 min through wavelength demodulation. Figure 8: (**a**) Fourier transform of transmission spectrum; (**b**) comparison of transmission spectrum before and after filtering. Figure 7: The measurement platform of the magnetic field. The performance comparison of the proposed sensor with the MF-based optical fiber MZI sensors in recent years is given in Table 2. From Table 2, the sensitivity and the measurement range of [21; 26; 27; 28] are lower than that of the structure proposed in this paper, and although the sensitivity of [29] is higher than that of the proposed sensor, the measurement range is only from 0.024 to 0.2 Gs and the glue immersion method is adopted. In addition, only the basic fusing structure is used in this paper, and the sensitivity of the sensor can be further improved through the methods of tapering, bending, and dislocation of SHDCF. The simple preparation process, low cost, and fast response make the sensor proposed in this paper a potential candidate in practical magnetic field measurement applications. Figure 10: The change in wavelength of the proposed sensor at a magnetic field of 0 Gs within 120 min; the illustration shows the change in transmission spectrum with time intervals of 30 min.