| The magnetic fluid composed of magnetic nanoparticles,liquid carrier and surfactant is a unique functional material.The surfactant-coated magnetic nanoparticles are uniformly dispersed in a stable liquid carrier.The magnetic fluid will be magnetized in a magnetic field environment,and the magnetic nanoparticles will gather together to change the refractive index of magnetic fluid.Due to the unique optical characteristics of magnetic fluid,coupled with the excellent characteristics of optical fiber sensors such as high sensitivity,corrosion resistance,compact size,light weight,simple structure,and not susceptible to the external environment,these characteristics are lacking in traditional magnetic field sensors such as fluxgate magnetometers,Hall sensors,and nuclear magnetic resonance field meters.Therefore,in recent years,the research of optical fiber magnetic field sensor based on magnetic fluid has received much attention.Most of the optic fiber magnetic field sensors that have been reported use complex structures,expensive fibers,fiber Bragg gratings,longperiod fiber gratings,etc.,to realize magnetic field sensing that eliminates temperature crosssensitivity.Using these fibers,fiber gratings,complex structures not only increase the cost but also cause the complexity of the system,as a result,this paper studies simple structures and without expensive optical fibers,fiber gratings to design optical fiber sensor,and the two-parameter matrix can be used to measure magnet and temperature accurately.The main research work of this paper are as follows:(1)Single-mode fiber,three-core fiber,four-core fiber,and no-core fiber were successfully prepared into the Mach-Zehnder sensing structure and Michelson sensing structure by using Furukawa S178 A fiber fusing machine,setting the parameters of tapered fusion,using FITEL S326 fiber cutting tool and the high vacuum resistance evaporation film plating machine silver film.(2)A magnetic field sensor based on Mach-Zehnder sensing structure and magnetic fluid is presented.The Mach-Zehnder sensing structure composed of three-core fiber sandwiched by two no-core fibers.The magnetic field and temperature characteristics of the sensor are experimentally demonstrated.By analyzing the experimental results,it is found that in the range of 0-16 m T magnetic field intensity,the temperature has almost no effect on the interference dip wavelength of the sensor.The wavelength of the sensor interference dip increases linearly with the magnetic field intensity,and the corresponding wavelength sensitivity is 68.57 pm/m T.However,temperature will affect the intensity of interference dip.The maximum magnetic field intensity sensitivity and the maximum temperature intensity sensitivity are-0.8287 d B/m T and 0.33896 d B/?,respectively.(3)An optical fiber magnetic field sensor structure is a four-core fiber sandwiched by two no-core fibers through in-line fusion tapering technique,formed a bi-tapered MachZehnder interferometer and then combined with MF.The temperature and magnetic field characteristics of the sensor are explored.The experiment results show that the four parameters of the wavelength sensitivity of the two interference dips under the magnetic field and temperature can be obtained to form a two-parameter matrix,and the magnetic field and temperature can be measured simultaneously.The highest wavelength sensitivity under magnetic field and temperature are 264.29 pm/m T and-112 pm/?,respectively.(4)Two no-core fibers are respectively connected to the ends of the four-core fiber,and the end face of last no-core fiber is coated by silver to form Michelson sensing structure,Then the sensing structure combined with MF is achieved.The temperature and magnetic field characteristics of the sensor are studied in detail.It can be seen from the experimental results that the sensor has a wide measurement range(0-36 m T).In low magnetic field(0-18 m T),it can be affected by temperature,and the influence of temperature on the sensor can be eliminated through the two-parameter matrix.At high magnetic fields(18-36 m T),it is almost unaffected by temperature and the corresponding intensity sensitivity is-1.20993 d B/m T.(5)The no-core fiber and multi-mode fiber are connected in a very simple fusion program and the end face of multi-mode is coated by silver film to form the Michelson fiber sensor and then combine with the magnetic fluid to form the optic fiber magnetic field sensor.The temperature and magnetic field intensity can be monitored rapidly by intensity modulation.The experimental results show that the maximum intensity sensitivity under the magnetic field is-1.03329 d B/m T in the range of 0.4-3.6 m T;The maximum intensity sensitivity at temperature is 0.55179 d B/?. |
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