Sensing Theory And Simulation Study Of A Novel Magnetic Fluid Photonic Crystal

Magnetic fluid,also called magnetic liquid,is a new type of functional material.It is a kind of colloid consisting of ultrafine magnetic nanoparticles(Fe3O4,MnFe2O4,etc)covered by surfactant(water,oil,etc)dispersed in suitable carried liquid.The magnetic particles in the magnetic fluid remain uniform for a long time in the gravity field without separation and precipitation.It exhibits better stability in nature.Howerver,in an applied magnetic field the magnetic nanoparticles will gradually aggregate to form magnetic chains along the direction of the applied magnetic field,it exhibits better magnetic tunability.Magnetic fluid can displayed many unite optical properties owing to the magnetic tunability.It has potential application in optical sensing technology.Through the further investigation,it was found that a photonic-crystal-like hexagonal ordered structure can be formed between the formed magnetic chains when the applied magnetic field exceeded a certain value.The structure has the properties of both magnetic fluid and photonic crystal.The paper focuses on the novel magnetic fluid photonic crystal,and the microstructure,magnetic tunability,optical property and sensing technology were studied.The main contents of the research are as follows.(1)The forming mechanism of the magnetic fluid photonic crystal was studied theoretically.A modular dynamics method based on non-spherical particle was presented to analyze the forming process of the magnetic fluid photonic crystal.The interaction of the magnetic particles and effect of the applied magnetic field were fully considered.Both translational motion and rotational motion of the magnetic nanoparticles were considered simultaneously.The molecular dynamics method based on rod-like particle was first used to simulate the microscopic movements of magnetic nanoparticles in the magnetic fluid.The Fortran programming language was used.The changing process of the magnetic fluid with the certain volume fraction(1%)in different magnetic fields was analyzed.The result showed that magnetic nanoparticles would aggregate to form a new type of magnetic fluid photonic crystal when the applied magnetic field intensity exceeded 180 Oe.The structure could be tuned in the range of 180 Oe-320 Oe,and in the process the average diameter of magnetic columns was decreased.(2)On the basis of the magnetic fluid photonic crystal microstructure,the optical properties were further analyzed.The model of magnetic fluid film was set,and the transmission property with the light parallel/perpendicular to the applied magnetic field was studied respectively.When the incident light is parallel to the direction of the applied magnetic field,probability models for the magnetic fluid film was set by Monte Carlo method.The transmission property at 1550 nm was analyzed,and it was found that the transmissivity would increase from 0.5944 to 0.6475.When the incident light is perpendicular to the direction of the applied magnetic field,the plane wave expansion method based on magnetic photonic crystal was used to compute the photonic bandgap.The result showed that the two photonic bandgaps of TE mode and TM mode all moved to higher frequency when the magnetic field was increased from 180 Oe to 320 Oe,the two bandwidths respectively decreased about 17%and 87%.(3)A magnetic fluid photonic crystal waveguide was designed.The tunable slow light property of the magnetic fluid photonic crystal was analyzed.A glass film with two slots was presented to be filled with magnetic fluid.Magnetic fluid photonic crystal waveguide could be formed when external magnetic field was applied to the film.The tunable slow light property was studied by changing the intensity or sweep rate of the applied magnetic field.The result showed that the guide mode appeared in magnetic fluid photonic crystal.When the sweep rate of the applied magnetic field is fixed,the working wavelength corresponding to the slow light region was blue-shifted.The group velocity below 0.35c could be obtained,and it displayed the best linear relationship between the working wavelength and applied magnetic field when the sweep rate of applied magnetic field was 10 Oe/s.In addition,the slow light property was also tuned by changing temperature.The working wavelength corresponding to the slow light region was red-shifted when the temperature was increased.(4)A magnetic fluid photonic crystal microcavity was presented.Magnetic field sensing system based on the magnetic fluid photonic crystal microcavity was designed,and the transmission property was analyzed.The result showed that when the deep of the microcavity structure was 6 ?m,the central wavelength of resonance peak would be blue-shifted from 12.38 pm to 8.25?m with increasing magnetic field.The maximum sensitivity of 24.3 nm/Oe was obtained.It was presented that the resonance peak was tuned in near-infrared region by reducing the deep of the microcavity structure.The result showed that when the deep of the microcavity structure was reduced to 0.94 ?m,the resonance peak appeared in near-infrared region,the central wavelength of would be blue-shifted from 1.528 ?m to 1.452 ?m with increasing magnetic field.The maximum sensitivity of 0.38 nm/Oe was obtained(5)A combined magnetic fluid photonic crystal and surface plasmon resonance sensor for magnetic field detection is presented.The magnetic tunability of the magnetic fluid photonic crystal was analyzed,and in the process the effect on the resonant characteristic was studied.The result showed that when the magnetic fluid photonic crystal was formed near the gold film,the surface plasmon wave could be modulated and the resonance angle would be changed.An evanescent wave would resonate with a surface plasmon wave at a wavelength of 1.8pm when the applied magnetic field exceeded 150 Oe.The resonance angle shifted from 79.2° to 85.1° when the applied magnetic field was increased from 150 Oe to 250 Oe.The obtainable sensitivity was 0.0612 deg/Oe?The magnetic fluid photonic crystal presented in the paper is a novel photonic crystal with magnetic tunability.The lattice constant can be tuned by changing the applied magnetic field.It caused the changes of optical properties.The magnetic fluid photonic crystal waveguide can be formed when the magnetic fluid is inserted into a film with two slots.The slow light can be realized.When magnetic fluid photonic crystal microcavity is applied in the optical sensing field,the magnetic field sensor can be realized in near-infrared and mid-infrared region.When magnetic fluid photonic crystal is combined with surface plasmon resonance technology,high sensitivity sensor can be realized by scanning the incident angle.