Novel Magnetic Field Sensing Methods And Magneto-optical Modulation Based On Magnetic Fluids

Magnetic fluid (MF) is a kind of homogeneous colloidal dispersion withnanoparticles, surfactant and a suitable liquid carrier, that is to say, magnetic fluid is akind of composite functional material with ferromagnetism, which have both themagnetism of the solid magnetic materials and the fluidity of liquid materials. And MFhas numerous unique optical properties owing to the dynamic microstructure undermagnetic field. This dissertation is mainly concerned with two magnetic field sensorsbased on the tunable refractive index of MF and the influence of the cyclical magneticfield to the transmission of MF based on the dynamic microstructure.As a typical property of MF, the tunable refractive index of MF is always theinteresting point of many researchers. We design two kinds of magnetic field sensingsystem utilized this typical property. One is V-shaped sensing system. The propagationof the emergent light passing through the index-tunable MF will be influenced when theexternally applied magnetic field is changed. So, measuring the location of the emergentlight on the detecting plane can be used to meter the strength of the externally appliedmagnetic field. This sensing system avoids many defects of the traditional sensors andthe inherent birefringence of magnetic field or current sensor based on Faraday Effect,has relatively simple structure, and can operate at any incident angle. Another iscapillary sensing system. When the laser beam passes the capillary filled with magneticfluid, owing to the four lens model constituted by capillary, the position of the focal linewill shift with the changing magnetic field strength. So the magnetic field strength canbe measured through detecting the position of the focal line. The system not only hasthe advantages of V-shaped sensing system, but also has advantages of miniaturizationof device, easy operation, and lower dosage of MFs. Detailed theoretical analysis of thesensing principle, accuracy and sensitivity of these two systems are conducted andverified by the experiments. In our experimental parameters and conditions, themaximum sensitivities are7.5mm/T and3.75mm/T for the V-shaped sensing systemand capillary sensing system, respectively.As another typical property of MF, the tunable magneto-modulation of MF is alsoalways the interesting point of many researchers. In this work, we study the quantitativerelation between the modulation characteristic and the period of magnetic field underexternally switchable magnetic field with various modulation periods. There is a transitional modulation period between the square-like and oscillation-like modulation,which is inversely proportional to the strength of magnetic field and the concentrationof MF. Furthermore, the smallest transitional modulation period of magnetic field of40s and the largest transitional modulation period of magnetic field of282s are obtained.The relation between the modulation characteristic and the period of magnetic field hasreference value and guiding meaning for designing the pragmatic photonic devicesutilized the square-like modulation property of MF.