Theoretical And Experimental Research On Magnetic Fluid Optical Current Sensing

Magnetic fluid has the magnetic properties of solid materials and the fluidity of liquid materials.Researchers have carried out extensive research in the fields of optical devices and sensors by combining the magnetic field sensitive characteristics with optical characteristics of magnetic fluid.Thanks to the advantages of good insulation performance,electrical isolation,small size and light weight,magnetic fluid optical current sensors have become a development direction of current sensing technology,which has important research value and broad application prospects.Theoretical and experimental researches were made on the physical properties and influence factors of magnetic fluid,magnetic fluid optical current sensor,optical power cable current sensing technology based on magnetic fluid,and temperature characteristics of optical power cable current sensor.All above work is able to provide theoretical and technical support for magnetic fluid optical current sensing technology applications.The main works of this thesis are presented as follows:(1)The influence mechanism of incident power on the optical transmission properties of magnetic fluid was studied,and the tunable refractive index properties of magnetic fluid and its sensing theory were studied.The optical transmission properties of magnetic fluid and their influencing factors were analyzed,and the linear and non-linear relationships between the transmitted power and the incident power of magnetic fluid were compared in the case of no magnetic field and the applied magnetic field.The variation in the transmitted power and transmittance with magnetic field intensity at different incident powers were studied theoretically and experimentally,the influence mechanism of incident power on the optical transmission properties of magnetic fluid was studied.The results show that when the incident power was large,the transmitted power was sharply reduced in the weak magnetic field regime,but it tends to saturate in the strong magnetic field regime.When the incident power was small,the transmitted power variation was relatively small,but approximately linear increase over a wide range of magnetic fields.The change rule of optical transmission properties with incident power and magnetic field intensity were analyzed and summarized,in the weak magnetic field sensing,by appropriately increasing the incident power,it is beneficial to improve the sensing performance of the film and increase the magnetic field measurement range.In the case of strong magnetic field sensing,by appropriately reducing the incident power,the transmitted power responds approximately linearly to a wide range of magnetic fields,providing important theoretical support for the design,parameter selection and optimization,and application research of magnetic fluid optical current sensors.The study of the incident power influence on the optical transmission properties of magnetic fluid provides a theoretical basis for the selection of the parameter range in the sensing applications.The tunable refractive index of magnetic fluid was theoretically studied.The interference principle and evanescent field energy theory of the sensor based on the tunable refractive index of magnetic fluid were analyzed.(2)The method to improve the performance of the magnetic fluid optical current sensor based on the optical transmission properties by optimizing the incident power was proposed,and the method to improve the performance of the magnetic fluid optical current sensor based on the tunable refractive index properties by using the single mode fiber S-shaped and core-offset fusion splicing structure was proposed.The theories of magnetic nanoparticle aggregation and Mie scattering in magnetic fluid were studied and the arrangement of magnetic nanoparticles with the magnetic field was analyzed.The magnetic fluid optical current sensor was designed and the magnetic fluid optical current sensing experiment system was set up.The method to eliminate the power fluctuation of the light source by using the dual optical path method was studied,and the variation of the transmitted power ratio with the magnetic field intensity was measured.The method to improve the sensitivity of the magnetic fluid optical current sensor by optimizing the incident power was proposed.The variation in the sensitivity of the magnetic fluid optical current sensor with the magnetic field intensity was measured at different incident powers.The results show that in weak magnetic field sensing,appropriately increasing the incident power can increase the sensitivity of the sensor;in strong magnetic field sensing,appropriately reducing the incident power can increase the the sensitivity of the sensor and increase the magnetic field measurement range.The sensing principle of the single mode fiber S-shaped and core-offset fusion splicing structure was theoretically studied.The magnetic fluid current sensor of the single mode fiber S-shaped and core-offset fusion splicing structure based on tunable refractive index properties was proposed.The sensor was fabricated and the experimental system was set up.The variation in the sensor characteristics with the magnetic field strength was measured.The results show that the interference valley wavelength of the sensor moved linearly to the long wavelength direction with the increase of the magnetic field intensity,and the sensitivity of the sensor was 33.14 pm/Oe.(3)The optical power cable current sensing method based on the magnetic fluid optical current sensor was proposed.The optical power cable sensing technology was analyzed,and the optical power cable current sensing structure based on magnetic fluid was proposed.The magnetic field distribution characteristics of the optical power cable and the selection of the sensor position were theoretically calculated and experimentally studied.The optical power cable current sensing method based on magnetic fluid was proposed.The optical power cable current sensing experiment system consisting of the optical signal and current generating module,the sensing module,the optical signal and current receiving module was established,and the optical power cable current was measured.The variation in the optical transmission properties of the optical power cable current sensor was measured.The results show that the transmittance of the sensor decreases monotonically with the optical power cable current,and has a good linearity.When the optical power cable current was 0?500 A,the sensitivity of the 200 ?m and 400 ?m optical power cable current sensors were-0.001004/A and-0.001499/A,the measurement errors were±1.0%and±2.0%,respectively.The optical power cable current sensor of the single mode fiber S-shaped and core-offset fusion splicing structure based on tunable refractive index properties of magnetic fluid was measured.The results show that the interference valley wavelength of the sensor moved to the long wavelength direction with the increase of the optical power cable current,and has a good linearity.When the optical power cable current was 0?500 A,the sensitivity of the sensor was 2.772 pm/A,and the measurement error was±0.03%.(4)Influence mechanism of temperature on magnetic fluid optical current sensor was studied.Brownian motion and thermal lens effect of the magnetic fluid optical current sensor was theoretically analyzed.The temperature characteristics of the magnetic fluid current sensor were theoretically studied,and the variation in the optical transmission properties of the sensor was measured as a function of temperature.The experimental system of the temperature influence on the optical power cable current sensor was designed and constructed,and the variation in the characteristics of the optical power cable current sensor with the optical power cable temperature was measured.The method to eliminate the influence of light source power fluctuation on the optical power cable current sensor by using the dual optical path method was proposed,and experimental system was designed and constructed to measure the variation of the transmitted power ratio of the dual optical path with the optical power cable current.The temperature characteristics of the magnetic fluid current sensor of the single mode fiber S-shaped and core-offset fusion splicing structure with tunable refractive index properties were studied,and variation in the the sensor characteristics with temperature was measured,the sensitivity of the sensor was 14.3 pm/?.The method for simultaneous measurement of current and temperature using the optical power cable current sensor of single mode fiber S-shaped and core-offset fusion splicing structure based on tunable refractive index properties and the elimination of temperature influence were realized.