| Magnetic fluids (MF), which is also called ferrofluid or magnetic liquid, is a new type of functional material. It has both the magnetism of solid magnetic material and fluidity of liquid material. It is a kind of stable colloid that the magnetic nanoparticles dressed with surfactant highly dispersed in one kind of carrier liquid.Magnetic fluids has so many unique properties that it develops quickly in various research area. The early study of magnetic fluids was in the 1960s, and now it goes deep into the areas of electronic, energy, aerospace, national defense, metallurgical machinery, chemical engineering and environment protection, instrumentation, health and medical community and so on. Nowadays, the research on the optical properties of the magnetic fluids is still hot research topic around the world.In the paper, the mainly research was the properties of magnetic fluid and the key technologies of its fiber Fabry-Perot(FP) sensor. The features and innovations of the paper were described as follow.(1) Theoretical and experimental study of the magnetic fluid microstructure were carried out simultaneously. The thesis proposed that the optical properties study of magnetic fluid should start from its essence, it meant to research the microstructure variation with or without an external magnetic field. In theoretical study, the particle model of magnetic fluid, the interaction among particles and the external interaction to the particle, was considered and analyzed, and then a proper model was established. Through comparing all kinds of micro particle simulation method, Monte Carlo simulation method was adopted to simulate the microstructure of MF using the Fortran programming language. The simulation result showed: the magnetic particles of magnetic fluid would flocculate weakly without no field; when under an external magnetic field, it would form chain-like structure along the direction of the magnetic field, the length of the chain-like structure would increase with increase of the magnetic field strength, but it would be broken by the increase of temperature. In experimental study, the fabrication of magnetic fluid film in micrometer was resolved, and the experiment system to research the microstructure with or without magnetic field dynamically was designed and established. Chemical etching method was adopted to successfully fabricate the magnetic fluid film with smooth, uniform, micron-sized, by using the self-design polymethyl methacrylate(PMMA) seal operation box. The thickness of MF film could be low down to 6μm. And the experiment system to dynamically research the microstructure of magnetic fluid was mainly composed of an microscope and the self-design water-cooling magnetic field generator, it could provide a uniform magnetic field more than 500Gs and ensure the space of sample observation uniform temperature. The experiments showed that the chain-like structure formed along the direction of magnetic field and its length increased with the increase of the magnetic field, and also it could be broken with increase of temperature. It proved that the simulations of the microstructure were effective and feasible.(2) Base on the microstructure simulation result above, theoretical and experimental study of the magnetic fluid optical properties was carried out. Base on the microstructure model established before, it was extended infinitely in the directions of X axis and Y axis, and finitely in the direction of Z axis, to obtain the magnetic film model approaching to the actual size. According to the Mie scattering theory, it used the probability model of the light through the film to simulate the transmit process of light, and then achieved the spectrum at the wavelength of 1μm～15μm, when the magnetic field was in different direction, or the magnetic fluid film with different thickness and different concentration. In experiment, a collimating frame was designed to maintain a proper position of the pair of optical fiber collimators. The transmission of the two collimators could be up to 86%. Besides the optical path, the optical properties research system including optical power detector module, data acquisition system, was designed and established. It could achieve optical properties research of MF at 1550nm. With the permission of the certain error, the experiment result was identical to the simulation.(3) Based on the magnetic fluid optical properties, a novel magnetic fluid-filled fiber FP magnetic field/current sensor which was the combination of the magnetic fluid and fiber FP interferometer was proposed. The fabrication equipment was designed and achieved, which was consisted of a microscope and a pair of six dimensional adjusting frame. Its accuracy was up to the 0.5μm. The research on air-filled fiber FP sensor and alcohol-filled fiber FP sensor effectively proved the feasibility of the sensor structure and the bonding way. It effectively reduced the influence of temperature and the seal technology was obtained. And the magnetic fluid-filled fiber FP sensor was made. Under a certain temperature of 28℃, its sensitivity was 0.046nm/Gs in theory, and 0.0431nm/Gs in experiment, with an external magnetic field at the range from OGs to 400Gs.(4) To resolve the influence on the magnetic fluid optical properties by temperature and magnetic field simultaneously and improve the magnetic fluid-filled fiber FP sensor, the fiber Bragg grating(FBG) was adopted to design a novel fiber Bragg grating Fabry-Perot(FBG-FP) sensor scientifically and reasonably which was combined with the previously made magnetic fluid-filled fiber FP sensor. The FBG could measure the temperature because of its temperature sensitivity, and then the temperature could be obtained to compensate the temperature influence. The sensing principle is derived, and then the novel structure could not only compensate the temperature influence, but also measure the temperature and magnetic field at the same time, which was proved by the simulation result. And the sensitivities of the temperature and magnetic field were 0.0456nm/Gs and 0.0133nm/℃ respectively.The thesis effectively researched the microstructure variation with the temperature and magnetic field, and also the related optical properties. And then the magnetic fluid was filled into the cavity of the fiber FP to form a novel magnetic field/current sensor. And it could measure the magnetic field at a certain temperature. The improvement of magnetic field sensor was made by adopting a fiber Bragg grating. The simulation result proved that the FBG could measure the temperature around the sensor to compensate the temperature influence. And it was also proved to be a double parameters measurement, temperature and magnetic field, simultaneously. |
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