| Frequency-shifted interferometry fiber cavity ring-down（FSI-FCRD）sensing technology has become a new research hotspot in the field of fiber-optic cavity ring-down sensing due to its advantages of high sensitivity,high stability and low cost.And it has been initially applied in single-point magnetic field intensity detection.However,in practical applications,multi-point magnetic field detection is often required and the influence of ambient temperature on the magnetic field detection needs to be considered.Therefore,it is very important theoretical and practical significance to carry out FSI-FCRD magnetic field and temperature sensing methods and their application in multi-point magnetic field detection.In order to improve the accuracy of magnetic field detection,this thesis studies the thermal effect of magnetic fluid,and proposes a single-point and multi-point magnetic field detection method under the condition of considering the thermal effect of magnetic fluid.At the same time,in order to improve the stability of the magnetic field sensing system,this thesis proposes a FSI-FCRD magnetic field and temperature sensing technology based on the D-type optical fiber as the sensor head.The relevant research results obtained are as follows:1.This thesis presents a temperature measurement method based on FSI-FCRD sensing technology.A tapered fiber wrapped by the magnetic fluid（MF）is used as the sensor head,and temperature sensing is realized by measuring the ring-down distance in the range of-10 ℃ to 50 ℃.The experimental results show that the temperature sensor based on the FSI-FCRD sensing technology has good linear response characteristics and its sensitivity can be as high as-1.71×10-3/（km·℃）,which shows that the MF-based sensor head has the thermal effect that cannot be ignored,and the thermal effect of the MF should be considered in the magnetic field detection.2.A single-point magnetic field sensor with FSI-FCRD considered the thermal effect of MF was proposed in this thesis.The temperature controller based on the Peltier effect was used to eliminate the influence of the thermal effect of the MF on the magnetic field detection,and the accuracy of the magnetic field detection was improved,and the D-shaped fiber coated by the MF was used as the sensor head to enhance the evanescent field effect and mechanical strength of the sensor.At a constant temperature of 20℃,the sensor has a sensitivity of 2.53×10-3(km-1·Gs-1)and a system stability of0.146%,which were all better than those of traditional FCRD magnetic field sensors based on the evanescent field effect.In addition,compared with the traditional FCRD magnetic field sensors,the FSI-FCRD magnetic field sensor has the advantage of low cost because it uses a cheaper continuous wave laser and a low-speed detector.Therefore,the proposed sensor in this thesis has a good application prospect in the field of magnetic field detection.3.According to the thermal effect of the MF,a multi-point temperature sensing scheme based on FSI-FCRD technology was proposed in this thesis,and a dual-point temperature sensing experimental setup was built up to verify it.The experimental results show that the dual-point sensors proposed in this thesis has good linear response characteristics in the range of-10 ℃ to 30℃,and can obtain the sensitivities of temperature as high as-0.0038/（km·℃）and-0.0062/（km·℃）.Compared with the traditional FCRD multi-point temperature sensor,the proposed multi-point temperature sensor in this thesis not only solves the problem of high cost,but also can effectively improve the sensitivity and stability of the sensing system,and can directly obtain the position information of each sensor.This work provides a practical solution for high-sensitivity measurement of multi-point temperature.4.This thesis reports a FSI-FCRD multi-point magnetic field sensing scheme that can eliminate temperature cross-sensitivity,and an experimental verification of two-point magnetic field sensing method is conducted.A temperature controller based on the Peltier effect was used to eliminate the temperature cross-sensitivity problem and the D-shaped fiber coated with MF was used as the sensor head to improve the stability of the sensing system.The baseline stability of the proposed dual-point sensors at 20 ℃ can reach 0.15%and 0.18%,respectively.In the magnetic field range of 0 to 250 Gs,the sensitivities were 6.7894×10-4d B/Gs and 7.4980×10-4d B/Gs,respectively.And the corresponding magnetic field detection limits were 2.56 Gs and 3.63 Gs.By verification the principle of dual-point magnetic field sensing experiment,the technical feasibility of the multi-point magnetic field detection scheme proposed in this thesis was verified,which provides a new method for high-sensitivity multi-point magnetic field detection. |
