| Optical Current Transducer (OCT) gets more attentions for its outstanding advantages on insulation and cost, etc. However, the troubles of the lower signal-to-noise ratio and the difficult manufacture processing of the general used magneto-optical materials, such as magneto-optical glass and the fiber optic gratings, hinder the application of OCT in the power system. It's an urgent need to search for the new type of sensing material for the power system to measure the electric current.Ferrofluid, also named magnetic fluid, is a colloidal suspension of magnetic nanoparticles diffused stably in liquid carrier. The ferrofluid film presents excellent magneto-optical properties when exposed to the external magnetic field. Previous studies on the application of ferrofluid in the electric current sensing show that the static and dynamic characteristics obviously exceed the living magneto-optical materials. Moreover, ferrofluid has higher sensitivity as the sensing element and it is convenient to manufacture. Whereas the studies on the magneto-optical effect of ferrofluid, especially the longitudinal magneto-optical effect still in its infancy, which restricted the practical process in the electric current sensing to a certain extent. The dissertation focuses on and systematical research on the basic features of the longitudinal magneto-optical effect in ferrofluid and its microscopic mechanisms of the effect.Firstly, as the research subject of the dissertation, aqueous ferrofluid is analyzed in the magnetic, optical and other properties. Combination with the non-symmetrical models of the dielectric tensor of the magnetic nanoparticles, the physical process of the longitudinal and the interaction mechanism of the influence factors are clarified. The formation theory is improved by the models, which also be validated by the Jones matrix. Secondly, the non-reciprocity of the longitudinal magneto-optical effect for ferrofluid is investigated more comprehensively by the dynamic testing on the self-developed platform. Lastly, the dynamic process of agglomeration in ferrofluid is analyzed based on the fundamental of the dissipative particle dynamics. The relationship of the disordered formation of the agglomeration and the related parameters with the field intensity and ferrofluid, and it also provides a sound evidence for the mechanism of the evolution of the chain-formation in ferrofluid and the magneto-optical effect. The main innovative results of the dissertation include:?The static and the dynamic characteristics are investigated systematically for the longitudinal magneto-optical effect of ferrofluid. The results show that the magneto-rotation effect of ferrofluid response soundly not only to the alternating magnetic field but also to the pulse field. The static property of the magneto-optical effect on the constant magnetic field presents excellent linearity.?The reciprocity of the longitudinal magneto-optical effect in ferrofluid is firstly investigated into the system. The response of ferrofluid modulated by the longitudinal magnetic field does not change with the direction of the modulating magnetic field.. General laws of the magneto-optical effect are revealed for ferrofluid under the stationary and the alternating field. Based on the analysis to the model of the asymmetric dielectric-tensor with the basic equations of the electromagnetic waves, it can be attributed to the dissymmetry of the off-diagonal terms in dielectric-tensor matrix. A measurement system with a double reflection light path is designed to reduce the measurement error due to the power fluctuation of light source and to improve the anti-interference ability.?Electromagnetic model of the longitudinal magneto-optical effect in ferrofluid is modified and the physical process is studied for the linear polarized light as electromagnetic waves propagated in ferrofluid with the chain-like formation under the external magnetic field. The Jones matrix is presented to describe the longitudinal magneto-optical effect in ferrofluid and the relaxation process of ferrofluid exposed to the magnetic field is analyzed.?Based on the coarse-graining model of ferrofluid, Dissipative Particle Dynamics simulations are performed in three-dimensional space to investigate the morphological characters of agglomeration. The long-range interactions of magnetic nanoparticles are converted into short-range ones by Ewald summation method to avoid the external overlap between dissipative and magnetic particles in Lennard-Jones potential model. The characteristics of the agglomeration under the external magnetic field is analyzed and the results confirmed that the disordered formation in ferrofluid. The relationship of the diameters and the lengths of the chain-like formation with the field strength, the mass concentration of the magnetic nanoparticles and the scale of the beads are analyzed. |
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