Research on heat dissipation characteristics of magnetic fluid bearings under multiple field coupling effects

This paper analyzes the sources of heat losses in magnetic fluid bearings,proposes various cou-pling relationships of physical fields,divides the coupled heat transfer surfaces while ensuring the continuity of heat flux density,and analyzes the overall heat dissipation pathways of the bearings.By changing parameters such as input current,rotor speed,and inlet oil flow rate,the study applies a multi-physics field coupling method to investigate the influence of different parameters on the temper-ature field and heat dissipation patterns of the bearings,which is then validated through experi-ments.This research provides a theoretical basis for the optimal design of magnetic fluid bearing sys-tems.

Multi-band polarization switch based on magnetic fluid filled dual-core photonic crystal fiber

The research of high-performance polarization controllers is of great significance for expanding the application field of polarization optics. Here, a polarization switch is demonstrated by using a dual-core photonic crystal fiber(DCPCF)with four symmetrical air holes, placed above and below each core, filled with magnetic fluid(MF). The switch, which utilizes a magnetic field to change the coupling length ratio of the x and y polarization modes, enables dynamic tuning of the polarization state and extinction ratio. Numerical results show that when the working length is 36.638 mm, the magneto–optical polarization switch can operate in four communication bands, i.e., 1509 nm to 1520 nm, 1544 nm to1556 nm, 1578 nm to 1591 nm, and 1611 nm to 1624 nm. Moreover, the extinction ratio(ER) is greater than 20 d B in the fiber length range of 38.5 mm to 38.7 mm, indicating that the device has a good fault tolerance for the interception of the fiber length.

Nanosized As_2O_3/Fe_2O_3 complexes combined with magnetic fluid hyperthermia selectively target liver cancer cells

AIM:To study the methods of preparing the magnetic nano-microspheres of Fe2O3 and As2O3/Fe2O3 complexes and their therapeutic effects with magnetic fluid hyperthermia(MFH). METHODS:Nanospheres were prepared by chemical co-precipitation and their shape and diameter were observed.Hemolysis,micronucleus,cell viability,and LD50 along with other in vivo tests were performed to evaluate the Fe2O3 microsphere biocompatibility.The inhibition ratio of tumors after Fe2O3 and As2O3/Fe2O3 injections combined with induced hyperthermia in xenograft human hepatocarcinoma was calculated. RESULTS:Fe2O3 and As2O3/Fe2O3 particles were round with an average diameter of 20 nm and 100 nm as observed under transmission electron microscope.Upon exposure to an alternating magnetic field(AMF),the temperature of the suspension of magnetic particles increased to 41-51℃,depending on different particle concentrations,and remained stable thereafter.Nanosized Fe2O3 microspheres are a new kind of biomaterial without cytotoxic effects.The LD50 of both Fe2O3 and As2O3/Fe2O3 in mice was higher than 5 g/kg.One to four weeks after Fe2O3 and As2O3/Fe2O3 complex injections into healthy pig livers,no significant differences were found in serum AST,ALT,BUN and Cr levels among thepigs of all groups(P>0.05),and no obvious pathological alterations were observed.After exposure to alternating magnetic fields,the inhibition ratio of the tumors was significantly different from controls in the Fe2O3 and As2O3/Fe2O3 groups(68.74% and 82.79%,respectively; P<0.01).Tumors of mice in treatment groups showed obvious necrosis,while normal tissues adjoining the tumor and internal organs did not. CONCLUSION:Fe2O3 and As2O3/Fe2O3 complexes exerted radiofrequency-induced hyperthermia and drug toxicity on tumors without any liver or kidney damage. Therefore,nanospheres are ideal carriers for tumortargeted therapy.

Motion State Analysis and Seal Ability Study on the Magnetic Fluid Seal of Reciprocating Shaft

The authors have studied the motion mechanism of the magnetic fluid in a reciprocating seal gap,on the basis of which the authors obtain an anti pressure formula of the reciprocating shaft magnetic fluid seal from general Navier Stokes equation.In order to verify the correctness of the anti pressure formula,the authors have calculated the magnetic field distribution of seal structure and have gotten the maximum still anti pressure.Finally,the authors have verified the influence of speed and stroke on the seal anti pressure.

Sealing mechanism of magnetic fluids

Sealing is one of the most successful apphcatious of magnetic fluids. However, the sealing pressure difference is not satisfactory. This paper theoretically analyzes the mechanism of magnetic fluids sealing. Main factors that have significant effects on the sealing ability include viscous stress on the interracial surface, magnetic surface tension, and the shape of the interracial surface. The sealing pressure with magnetic fluids decreases with increase of rotational speed. Experiments were carried out to study the stability of the interface between magnetic fluids and water. It has been shown that stability of the interface will be damaged by washing of water when the relative flow between water and magnetic fluid becomes turbulent.

All-fiber optical modulator based on no-core fiber and magnetic fluid as cladding

An all-fiber optical modulator, which is composed of a piece of no-core fiber spliced between two sections of singlemode fibers and uses magnetic fluid（MF） as the cladding of the no-core fiber section, is proposed and investigated experimentally. Due to the tunable refractive index and absorption coefficient of MF, the output intensity can be modulated by controlling an applied magnetic field. The dependences of the modulator＇s temporal response on the working wavelength,the magnetic field strength（H）, and the MF＇s concentration are investigated experimentally. The results are explained qualitatively by the dynamic response process of MF under the action of a magnetic field. The findings are helpful for optimizing this kind of modulator.

Characteristics of a magnetic fluid seal and its motion in an axial variable seal gap

With suitable assumptions a hydrodynamic model for the magnetic fluid motion in an axial variable gap seal was con- structed, and the solution to the equations of the model was deduced. The characteristics of a magnetic fluid seal and its motion, including the speed and pressure distribution, and the seal capacity of a magnetic fluid rotating seal were systematically described. The factors affecting seal capacity and ways to improve seal capacity based on the hydrodynamic model are discussed. The basic condition for dynamic seal availability is presented. The rotating speed and radius of the shafts should be decreased. The work can provide proof of a seal design or suggest ways to improve the seal capacity of magnetic fluid seals.

Coaxial Twin-shaft Magnetic Fluid Seals Applied in Vacuum Wafer-Handling Robot

Compared with traditional mechanical seals,magnetic fluid seals have unique characters of high airtightness,minimal friction torque requirements,pollution-free and long life-span,widely used in vacuum robots.With the rapid development of Integrate Circuit（IC）,there is a stringent requirement for sealing wafer-handling robots when working in a vacuum environment.The parameters of magnetic fluid seals structure is very important in the vacuum robot design.This paper gives a magnetic fluid seal device for the robot.Firstly,the seal differential pressure formulas of magnetic fluid seal are deduced according to the theory of ferrohydrodynamics,which indicate that the magnetic field gradient in the sealing gap determines the seal capacity of magnetic fluid seal.Secondly,the magnetic analysis model of twin-shaft magnetic fluid seals structure is established.By analyzing the magnetic field distribution of dual magnetic fluid seal,the optimal value ranges of important parameters,including parameters of the permanent magnetic ring,the magnetic pole tooth,the outer shaft,the outer shaft sleeve and the axial relative position of two permanent magnetic rings,which affect the seal differential pressure,are obtained.A wafer-handling robot equipped with coaxial twin-shaft magnetic fluid rotary seals and bellows seal is devised and an optimized twin-shaft magnetic fluid seals experimental platform is built.Test result shows that when the speed of the two rotational shafts ranges from 0-500 r/min,the maximum burst pressure is about 0.24 MPa.Magnetic fluid rotary seals can provide satisfactory performance in the application of wafer-handling robot.The proposed coaxial twin-shaft magnetic fluid rotary seal provides the instruction to design high-speed vacuum robot.

Numerical Analysis of Magnetic Fluid Sealing Performance

The sealing performance of magnetic fluid is related to the magnetic fluid itself. Many factors can influence the magnetic field and the seal pressure differences of magnetic fluid seals, such as the sealing gap, the shaft eccentricity, the shaft diameter, the volume of the magnetic fluid and the centrifugal force. These factors are analyzed by numerical computation. When the seal material and structure are the same, the seal pressure difference is directly proportional to the magnetic field intensity and the saturation magnetization of the magnetic fluid. The sealing performance of the magnetic fluid will reduce with the increase of the sealing gap and shaft eccentricity. The sealing performance will increase with the volume of the magnetic fluid and decrease with the increase of the shaft diameter taking gravity into account. The increase of the shaft diameter is the same as the reduction of the volume of the magnetic fluid. The magnetic fluid cross-section can change because of the centrifugal force. Some improvements can reducc the influence of the centrifugal force. The centrifugal force can be utilized to improve the sealing performance.

Tunable magneto optic modulation based on magnetically responsive nanostructured magnetic fluid

Magnetic fluid is a kind of functional composite material with nanosized structure and unique optical properties. The tunable magneto-optic modulation of magnetic fluid under external magnetic field, achieved by adjusting the polarization direction of incident light, is investigated theoretically and experimentally in this work. The corresponding modulation depth and response time are obtained. The accompanying mechanisms are clarified by using the theory of dichroism of magtietic fluid and the aggregation/disintegration processes of magnetic particles within magnetic fluid when the external magnetic field turns on/off.

A New Design of Magnetic Fluid Seal for Liquids

Direct contract between the sealed liquid and the magnetic fluid in a dynamic system under magnetic field may lead to an unstable interface, consequently, break down the seal. Aiming at this problem, a new magnetic fluid seal (MFS) was developed. In this new MFS, a soft iron bushing with high permeability was introduced on the shaft and nonferrous shields were installed beside the bushing and the pole pieces. The parameters of the bushing and the shields were optimized in a seal simulation facility The results show that the bushing with a thickness of 7 mm and shields with a width of 8 mm are best for sealing a shaft 20 mm in diameter. The MFS designed based on the optimum parameters shows good performance and long life span for sealing lubricating oil.

A Multi-Parameter Sensor Based on Cascaded Photonic Crystal Cavities Filled with Magnetic Fluid

A kind of photonic crystal (PC) micro-cavity sensor based on magnetic fluid (MF) filling is designed with simulation model. Generally, many sensors’ designs are based on a universal temperature in the whole structure. However, strong photothermal effect in high Q micro-cavities will lead to different temperatures between cavities and environment inevitably. In many theoretical PC sensor designs, researchers neglected the different temperature between environment and cavities. This simple hypothesis will probably lead to failure of sensor design and get wrong temperature. Moreover, few theoretical or experimental works have been done to study optical cavity’s heating process and temperature. We propose that researchers should take seriously about this point. Here, the designed cascaded micro-cavity structure has three spectral lines and a reversible sensitivity matrix, which can simultaneously detect magnetic field, ambient temperature and MF micro-cavity temperature. It can solve the magnetic field and temperature cross-sensitivity problem, and further, distinguish the different temperatures of environment and magnetic fluid cavities. The influence of hole radius and slab thickness on the depth and Q value of the resonant spectral line are also studied. Responses of three dips to magnetic field, ambient temperature and MF micro-cavity temperature are simulated, respectively, where dip 1 belongs to MF cavity 1, dip 2 and dip 3 belong to MF cavity 2. The obtained magnetic field sensitivities are 2.89 pm/Oe, 4.57 pm/Oe, and 5.14 pm/Oe, respectively;the ambient temperature sensitivities are 65.51 pm/K, 50.94 pm/K, and 58.98 pm/K, respectively;and the MF micro-cavity temperature sensitivities are −14.41 pm/K, −17.06 pm/K, and −18.81 pm/K, respectively.

PREPARATION OF Fe_3O_4/PSt MAGNETIC PARTICLES IN THE PRESENCE OF MAGNETIC FLUID IN ETHANOL/WATER MIXTURE

Fe_3O_4/Polystyrene(PSt) magnetic particles with core/shell structure have been prepared in thepresence of Fe_3O_4 magnetic fluid in ethanol/water medium by dispersion polymeriation of styrene. A Fe_3O_4particle formation mechanism was proposed. According to this mechanism, the size of particle nuclei isdetermined by the extent of aggregation of Fe_3O_4 /oligomer. Magnetic particles with diameter ranging from 5to 200 μm were prepared under different reaction conditions. Some polymerization parameters such as theconcentration of monomer, stabilizer, initiator, and ethanol which affect particle size and size distribution arediscussed and their effect on particle formation are explained by the proposed mechanism.

Laser beam shaping with magnetic fluid-based liquid deformable mirrors

A new controllable laser beam shaping technique is demonstrated, where a magnetic fluid-based liquid deformable mirror is proposed to redistribute the laser phase profile and thus change the propagation property of the beam. The mirror is driven by an inner miniature actuator array along with a large outer actuator. The inner actuator array is used for deforming the magnetic fluid surface, while the outer actuator is used to linearize the fluid surface response and amplify the magnitude of the deflection. In comparison to other laser beam shaping techniques, this technique offers the advantages such as simplicity, low cost, large shape deformation, and high adaptability. Based on a fabricated prototype of the liquid deformable mirror, an experimental AO system was set up to produce a desired conical surface shape that shaped the incident beam into a Bessel beam. The experimental results show the effectiveness of the proposed technique for laser beam shaping.

Stability of plane-parallel flow of magnetic fluids under external magnetic fields

In this work,we present a theoretical study on the stability of a two-dimensional plane Poiseuille flow of magnetic fluids in the presence of externally applied magnetic fields.The fluids are assumed to be incompressible,and their magnetization is coupled to the flow through a simple phenomenological equation.Dimensionless parameters are defined,and the equations are perturbed around the base state.The eigenvalues of the linearized system are computed using a finite difference scheme and studied with respect to the dimensionless parameters of the problem.We examine the cases of both the horizontal and vertical magnetic fields.The obtained results indicate that the flow is destabilized in the horizontally applied magnetic field,but stabilized in the vertically applied field.We characterize the stability of the flow by computing the stability diagrams in terms of the dimensionless parameters and determine the variation in the critical Reynolds number in terms of the magnetic parameters.Furthermore,we show that the superparamagnetic limit,in which the magnetization of the fluids decouples from hydrodynamics,recovers the same purely hydrodynamic critical Reynolds number,regardless of the applied field direction and of the values of the other dimensionless magnetic parameters.

Tunable negative-index photonic crystals using colloidal magnetic fluids

The model of using colloidal magnetic fluid to build tunable negative-index photonic crystal is established. The effective permittivity εe and permeability μe of the two-dimensional photonic crystal are investigated in detail. For transverse magnetic polarization, both εe and μe exhibit a Lorentz-type anomalous dispersion, leading to a region where εe and μe are simultaneously negative. Then, considering a practical case, in which the thickness of photonic crystal is finite, the band structures for odd modes are calculated by the plane wave expansion method and the finite-difference time-domain method. The results suggest that reducing the external magnetic field strength or slab thickness will weaken the periodic modulation strength of the photonic crystal. Simulation results prove that the negative-index can be tuned by varying the external magnetic field strength or the slab thickness. The work presented in this paper gives a guideline for realizing the flat photonic crystal lens with tunable properties at optical frequencies, which may have potential applications in tunable near-field imaging systems.

Magneto and Electro-Optic Intensity Modulator Based on Liquid Crystal and Magnetic Fluid Filled Photonic Crystal Fiber

We propose a novel light intensity modulator based on magnetic fluid and liquid crystal（LC） filled photonic crystal fibers（PCFs）. The influences of electric and magnetic fields on the transmission intensity are theoretically and experimentally analyzed and investigated. Both the electric and magnetic fields can manipulate the molecular arrangement of LC to array a certain angle without changing the refractive index of the LC. Therefore, light loss in the PCF varies with the electric and magnetic fields whereas the peak wavelengths remain constant. The experimental results show that the transmission intensity decreases with the increase of the electric and magnetic fields. The cut-off electric field is 0.899 V/um at 20 Hz and the cut-off magnetic field is 195 m T. This simple and compacted optical modulator will have a great prospect in sensing applications.

Dysprosium Modification of Cobalt Ferrite Ionic Magnetic Fluids

Dysprosium composite cobalt ferrite ionic magnetic fluids were prepared by precipitation in the presence of Tri-sodium citrate. Influence of dysprosium modification on magnetic property is studied. The result shows that magnetic response toward exterior magnetic field can be improved by adding Dy3+. Studies also show that the increase of reaction temperature may improve the modification effect of dysprosium. By adding dysprosium ions, the average diameter of the magnetic nanoparticles will be decreased evidently. It is clear that the particles appear as balls. Cobalt ferrite with sizes of 12-15 nm, rare earth composite cobalt ferrite with sizes of 6-8 nm.

Preparation of Rare-Earth Composite Ferrite Magnetic Fluid

Water-based rare-earth ferrite (Re xFe 3- xO 4)magnetic fluids were prepared by chemical co-precipitation method. The result shows that saturation magnetic intensity of ferrite magnetic fluids can be improved by adding Dy 3+ and the saturation magnetic intensity will reach the highest if n(Fe)∶n(Dy 3+ )=30∶1. The modification and formation mechanism of Re xFe 3- xO 4 particles is discussed in detail. The physicochemical properties are investigated by the Gouy magnetic balance, IR, TEM, XRD, and EDX, etc.

Theory analyses and applications of magnetic fluids in sealing

Magnetic fluids are the suspensions composed of magnetic nanoparticles,surfactants,and non-magnetic carrier liquids.Magnetic fluids are widely used in various fields,especially in sealing,because of their excellent features,including rapid magnetic response,flexible flow ability,tunable magneto-viscous effect,and reliable self-repairing capability.Here,we provide an in-depth,comprehensive insight into the theoretical analyses and diverse applications of magnetic fluids in sealing from three categories:static sealing,rotary sealing,and reciprocating sealing.We summarize the magnetic fluid sealing mechanisms and the development of magnetic fluid seals from 1960s to the present,particularly focusing on the recent progress of magnetic fluid seals.Although magnetic fluid sealing technology has been commercialized and industrialized,many difficulties still exist in its applications.At the end of the review,the present challenges and future prospects in the progress of magnetic fluid seals are also outlined.