The Research And Application Of The Magnetic Fluid Birefringence Properties

Magnetic fluid is a colloidal fluid composed by nanoscale magnetic particles suspended in a carrier fluid, which has not only the fluidity of carrier fluid but also the magnetism of magnetic particles. Thus it shows a lot of unique special physical properties and superficial phenomenon. Recently, the optical properties of magnetic fluid have attracted attentions by scholars because of thier magnetic field tunable characteristics. Many optical sensors have been designed based on the birefringence properties of magnetic fluid, such as tunable birefringent filters, optical attenuators, optical switches and so on. Therefore, the birefringence properties of magnetic fluid have important significance on both scientific research and applications, and it is significance to research the theory and the properties of the magnetic fluid birefringence properties. Considering that, it is necessary to enhance the theoretical research and performance of its birefringence.On the basis of a large number of domestic and foreign literatures, the following research work is finished in this thesis.(1) Through the Monte Carlo simulation method and experimental observation method, the three-dimensional microstructure was analyzed on the micro level. Moreover, the effect of the different magnetic field intensity on the micro structure of the magnetic liquid was obtained. Through the analysis of magnetic structure from the plane views parallel and perpendicular to the direction of the magnetic field, at last. the influence of magnetic field on the anisotropy of the magnetic fluid structure was summarized.(2) The formula of magnetic birefringence was derived based on the simulated magnetic structure. The relationship between the magnetic birefringence values and the intensity of the magnetic field was analyzed by the simulation, and the sensitivity of the magnetic fluid birefringence could be 1.25×10-6/Gs when the magnetic field was 200Gs～500Gs, and the sensitivity was 0.26×10-6/Gs when field was 200Gs～500Gs. Therefore, the simulation provided theoretical basis for experimental study.(3) The birefringence properties of magnetic fluids were studied from the experiment.The magnetic measurement experiment system under the spatial light path and the fiber optical path were designed respectively. Thereinto, the measurement results under the spatial light path was compared with the existing reference curve, when the magnetic field strength was100Gs-600Gs, and the relative error was within ±10%. In optical fiber path, the experimental measurement could greatly reduce the measurement error caused by artificial alignment problem. Therefore, measured birefringence values would be more close to the actual value;(4) Based on the theory of the fiber loop mirror, the relationship between the magnetic birefringence characteristics and the period of the optical fiber output spectrum was derived. Then the relationship between the magnetic field environment and the fiber loop mirror output spectrum period was studied by theoretical simulation. And the resolution of the spectral period changed with the magnetic field intensity could be 107pm/Gs. Finally the results were verified by experiments, which realized the fiber-optical sensing applications by using the birefringence of magnetic fluid.Through this research, the magnetic liquid structure changes could be understood from the microcosm, and the optical birefringence properties of magnetic field could be explained essentially. In the future, the mechanism of birefringence could be combined with the optical fiber technology, and the application on the optical sensors (such as electromagnetic sensors) would be implemented.