MAGNETOSTRICTIVE MATERIAL RESEARCH

Rare earth-containing magneto-strictive material has caught theworld attention in recent yearsbecause of its amazing performan-ces:high magnetostrictive ratio,rapid response to mechanical be-havior,high rate of energy tran-sformation,etc.,which are vitalto sonar transducers,performersand brakes which,in turn,play

A STUDY ON THE MAGNETOSTRATIGRAPHY OF THE LOESS SECTION OF GARZ■

The loess section of Garzê lies to the west of Garzê County in Sichuan Province (31°38＇N, 99°59＇E). The top of the section is 3480 m a. s. 1.

YbBi:YIG石榴石单晶的磁光性能及其光纤电流传感器应用

Magneto optic(MO) fiber current sensors utility the Faraday effect of magneto op tic materials to sensing the magnetic(current)fields.The optical fiber sensors(O FS)offer great advantages of simple structure,high reliability,high accuracy and sensibility,immunity to electromagnetic interference.They are the most promised method to substitute the conventional current transducers(CTs),much attentions were focused on both domestic and abroad.Magneto optic properties of Faraday se n sing element have much affect on the performance of the optical fiber current se nsor.For used in the sensor system,MO materials with magneto optic characterist i cs of large Faraday rotation(FR)angle θ f ,low temperature sensibility,and suitable saturation field were general demanded. Development of MO materials is one of the most important problems of optical fiber current sensor research. In this paper,one mixed doped Bi substituted yttrium iron garnet crystal BiYb:Y I G, which has large and temperature stable FR angle,was grown from high temperatu re flux.By taking PbO+PbF 2 as the main flux,under the compositions of molar ra tio Y 2O 3:Yb 2O 3:Bi 2O 3:Fe 2O 3:(PbO+PbF 2+B 2O 3+CaCO 3)=7.64:1. 04:1.74:20.78:78:68.8,crystals of quite good quality were grown from melt flux,t he largest one has the size of 22mm×15mm×12mm.Magneto optic proprieties of Fa raday rotation angle and optical absorption spectrum of the BiYb:YIG crystal,expecial ly Y 2.289 Yb 0.246 Bi 0.465 Fe 5O 12 ,in the range of 0.7 1.9 μm waveband were measured.At λ =1.55μm,the BiYb:YIG crystal has special Fa raday rotation angle of -404deg/cm,temperature coefficient 4.2×10 -6 K -1 ,optical absorption coefficient 3.6cm -1 ,and figure of merit 25.8deg/dB . The results indicate that substituted with Bi 3+ can largely improve the Fa raday rotation of rear earth iron garnets.Because Faraday rotation angles of Yb 3Fe 5O 12 and Y 3Fe 5O 12 have opposite temperature dependency,ut ility the compensation effect of mix doped,co doped with some other ions,such a s Yb 3+ ,would decrease the temperature dependency of Bi substituted garnet. So the garnet crystal BiYb:YIG has high and temperature stable Faraday rotation an gle,very suitable to be used as Faraday effect materials for high sensibility an d temperature stable Optical fiber current sensors.Using BiYb:YIG as Faraday rot ation cell,a hybrid bulk crystal optical fiber current sensor was proposed and t ests under direct current(DC) and 50Hz alternating current(AC).The performance c haracteristics of the sensors system were:DC measurement,sensibility 0.01A, l inea rity 1.1%;AC measurement,sensibility 9.5A/mV ,accuracy ±1%,linearity 1.1%,dynam ic range 40dB.In conclusion,Faraday effect magneto optic optical fiber current sensors have higher sensibility and accuracy than conventional CTs.

JET装置运行条件下的阿尔芬波特性研究

JET装置运行在先进托卡马克区域,在先进托卡马克区域内存在着负磁剪切,s<0(s=rdq/dr),在正剪切和负磁剪切下理论上都发现了约束在α(α=-q2Rdβ/dr)引发气球模驱动的势β里的离散阿尔芬本征模(αTAE)。q是安全因子,β是等离子体压力与磁压力之比,R和r分别代表托卡马克的大半径和小半径。这些模式的耗散率都很小,很容易被高能量粒子激发成不稳定性模式。在现行的大型托卡马克(如:DⅢ-D,JET,JT-60U)中实验上已经观察到了许多阿尔芬现象,这种离散阿尔芬本征模式是一种去理解这些实验现象的潜在物理机制。

Effects of hot top pulsed magneto-oscillation on solidification structure of steel ingot

Achieving a uniform structure with few defects in heavy steel ingot is of high commercial importance. In this present work, in order to verify the potential of pulsed magneto-oscillation(PMO) applied in the production of heavy ingot, an induction coil was located at the hot top of the steel ingot to develop a novel technique, named hot top pulsed magneto oscillation(HPMO). The influences of HPMO on the solidification structure, macro segregation and compactness of a cylindrical medium carbon steel ingot with the weight of 160 kg were systematically investigated by optical microscope(OM) and laser induced breakdown spectroscopy original position metal analyzer(LIBSOPA-100). The results show that HPMO not only causes significant grain refinement and promotes the occurrence of columnar to equiaxed transition(CET) but also can homogenize the carbon distribution and enhance the compactness of the steel ingot. Therefore, HPMO technique has the potential to be applied in the production of heavy steel ingots on an industrial scale.

Magneto-Optical Trap of Cesium Atoms

We have trapped a cold sample of cesium atoms in a magneto-optical trap.The damped harmonic force of magneto-optical trap was used to capture and trap the cesium atoms directly from a room temperature vapor.About 1.5×10^(7) cesium atoms with a density of 3×10^(9) atoms/cm^(3) formed a 4mm^(3) cesium atomic cloud with temperature below 500μK.

Tensile properties and microstructure of 2024 aluminum alloy subjected to the high magnetic field and external stress

In order to explore the dependence of plasticity of metallic material on a high magnetic held,the effects of the different magnetic induction intensities（H = 0 T,0.5 T,1 T,3 T,and 5 T） and pulses number（N = 0,10,20,30,40,and 50） on tensile strength（σ;） and elongation（δ） of 2024 aluminum alloy are investigated in the synchronous presences of a high magnetic held and external stress.The results show that the magnetic held exerts apparent and positive effects on the tensile properties of the alloy.Especially under the optimized condition of H;=1 T and N;=30,the σ;and 8 are 410 MPa and 17% that are enhanced by 9.3% and 30.8% respectively in comparison to those of the untreated sample.The synchronous increases of tensile properties are attributed to the magneto-plasticity effect on a quantum scale.That is,the magnetic held will accelerate the state conversion of radical pair generated between the dislocation and obstacles from singlet to the triplet state.The bonding energy between them is meanwhile lowered and the moving flexibility of dislocations will be enhanced.At H;= 1 T and N;= 30,the dislocation density is enhanced by 1.28 times.The relevant minimum grain size is 266.1 nm,which is reduced by 35.2%.The grain rehning is attributed to the dislocation accumulation and subsequent dynamic recrystallization.The（211） and（220） peak intensities are weakened.It is deduced that together with the recrystallization,the hne grains will transfer towards the slip plane and contribute to the slipping deformation.

Nonreciprocal transmission of electromagnetic waves by three-layer magneto-optical mediums

We investigate the non-reciprocal transmission properties of a three-layer structure filled with magneto–optical medium and normal medium. Based on the transfer matrix method, we deduce the total transmission coefficient for a one-dimensional(1 D) structure with anisotropic mediums. When two-side layers with magneto–optical medium loaded in opposite external magnetic field, the time-reversal symmetry of transmission properties will be broken. Our numerical results show that the non-reciprocal transmission properties are influenced by external magnetic fields, incident angle, and thickness of the normal medium layer. Since the non-reciprocal properties can be easily realized and adjusted by the simple structure, such a design has potential applications in integrated circulators and isolators.

Band Gap Properties of Magnetoelectroelastic Grid Structures with Initial Stress

The propagation of elastic waves in magnetoelectroelastic grid structures is studied.Band gap properties are presented and the effects of the magnetoelectroelastic coupling and initial stress are considered.Numerical calculations are performed using the plane-wave expansion method.The results show that the band gap width can be tuned by the initial stress.It is hoped that our results will be helpful for designing acoustic filters with magnetoelectroelastic materials and grid structures.

Magneto-Micropolar流体方程组恰当弱解的存在性

采用类似于Caffarelli-Kohn-Nirenberg和Fanghua Lin等人的方法,证明了Magneto-Micropolar流体方程组恰当弱解的存在性.

Giant magneto impedance effect of Co-rich amorphous fibers under magnetic interaction

The quasi-metallic fibers were selected from 1 to 40 pieces and connected in parallel in this study.The giant magneto impedance(GMI)effect of Co-based melt extract fibers in the bundle mode was investigated,and the distribution of the surface circumferential magnetic field on the fibers was also analyzed.Such distribution was induced by the driving current,which gave rise to the circular magnetization process and the GMI effect.The improved GMI effect with much higher field sensitivity was observed in these fiber bundles.Results show that the field sensitivities of the four-fiber and six-fiber bundles reach 19.5 V·m·kA−1(at 1 MHz)and 30.8 V·m·kA−1(at 5 MHz).The circumferential magnetic field distributed throughout the fiber’s circumferential surface is rearranged and becomes uneven due to the magnetic interaction among fibers.There are both strengthened and weakened magnetic field parts around these fibers’surfaces.The strengthened magnetic field improves the circumferential domain magnetization of the surface,resulting in larger GMI effects.However,the weakened parts inhibit the circumferential magnetization process and,therefore,the GMI effect.This also induces greater magnetization damp because of the increased domain interactions under the strong skin effect.The co-effect between the magnetic domains and the circumferential magnetization induces the optimization of the GMI effect in the four-fiber bundles.The observed GMI effect proves that fibers in bundle form can modify the sensitivity of the GMI effect.Moreover,different fiber bundles could be tuned according to the working conditions in order to manipulate the GMI response.

Design and optimization of a semi-active suspension system for railway applications

The present work focused on the application of innovative damping technologies in order to improve railway vehicle performances in terms of dynamic stability and comfort. As a benchmark case-study, the secondary sus- pension stage was selected and different control techniques were investigated, such as skyhook, dynamic compensation, and sliding mode control. The final aim was to investigate which control schemes are suitable for optimal exploitation of the non-linear behavior of the actuators. The performance improvement achieved by adoption of the semi-active dampers on a standard high-speed train was evaluated in terms of passenger comfort. Different control strategies have been investigated by comparing a simple SISO （single input single output） regulator based on the skyhook damper ap- proach with a centralized regulator. The centralized regulator allows for the estimation of a near optimal set of control forces that minimize car-body accelerations with respect to constraints imposed by limited performance of semi-active actuators. Simulation results show that best results is obtained using a mixed approach that considers the simultaneous applications of model based and feedback compensation control terms.

Collapse of charge ordering in Bi_(0.5)Sr_(0.5)MnO_3 by cation disorder: a magnetic and structural investigation

The structure, transport, and magnetic properties of LaxBi0.5.xSr0.5MnO3 （LBSMO） （x=0.1 and 0.4） were studied through X-ray diffraction, magnetization, and electron spin resonance （ESR） measurements. The structural analysis showed that the LBSMO crystallized in an orthorhombic perovskite structure with Pbnm space group for x=-0.1 and Imma space group for x=0.4 and the highly polarizable 6s^2 lone pair of Bi^3＋ was the ttming factor for the structural variations. Magnetic studies revealed that the replacement of Bi ions by La ions resulted in the collapse high temperature charge ordering state of BSMO and it order Ferro Magnetically （FM） with Tc around 355 and 330 K for x=0.1 and 0.4, respectively. Both ESR, temperature and field dependant magnetization suggested that there was a coexistence of FM and the paramagnetic phases well below Tc and the FM and CO-AFM phases below 250 K of LBSMO.

Auxiliary Teeth Design to Reduce Short-Circuit Current in Permanent Magnet Generators

In this paper,a new auxiliary teeth structure is proposed for fault-tolerant permanent magnet(PM)generators,which can reduce the short-circuit currents.Firstly,the short-circuit current and the phase to phase isolation of the fault-tolerant generator are analyzed briefly.Secondly,the auxiliary teeth structure is optimized to improve fault-tolerant capability.Then,the PM generators with different stator structures are compared to evaluate the proposed auxiliary teeth structure.Four critical generator parameters are investigated,i.e.back-electromotive forces,short-circuit currents,stator magneto motive force(MMF)harmonics,and torque performances.The results show that the proposed structure has better fault-tolerant capability than the conventional two-layer windings.Moreover,the stator MMF harmonics can be suppressed.Furthermore,the cogging torque and torque ripple can be suppressed by adopting the proposed structure.Finally,the simulated results are given to validate the theoretical analysis.

New Analytical Study of the Effects Thermo-Diffusion, Diffusion-Thermo and Chemical Reaction of Viscous Fluid on Magneto Hydrodynamics Flow in Divergent and Convergent Channels

In this paper, the magneto hydrodynamic (MHD) flow of viscous fluid in a channel with non-parallel plates is studied. The governing partial differential equation was transformed into a system of dimensionless non-similar coupled ordinary differential equation. The transformed conservations equations were solved by using new algorithm. Basically, this new algorithm depends mainly on the Taylor expansion application with the coefficients of power series resulting from integrating the order differential equation. Results obtained from new algorithm are compared with the results of numerical Range-Kutta fourth-order algorithm with help of the shooting algorithm. The comparison revealed that the resulting solutions were excellent agreement. Thermo-diffusion and diffusion-thermo effects were investigated to analyze the behavior of temperature and concentration profile. Also the influences of the first order chemical reaction and the rate of mass and heat transfer were studied. The computed analytical solution result for the velocity, temperature and concentration distribution with the effect of various important dimensionless parameters was analyzed and discussed graphically.

Novel inspection of welded joint microstructure using magneto-optical imaging technology

A novel method for measuring differences of microstructure by advanced use of the Faraday magneto-optical effect is proposed. Two groups of YAG laser welds on Q235 have been investigated in order to compare MO imaging and traditional methods. Microstructure images have been compared with MO images, and MO diagrams display different colors and gray scales for the base metal, the weld zone, and the heat affected zone. Experimental results indicate that the welded joint microstructure can be inspected by MO imaging without metallographic preparation.

Coherent population trapping magnetometer by differential detecting magneto–optic rotation effect

A pocket coherent population trapping（CPT） atomic magnetometer scheme that uses a vertical cavity surface emitting laser as a light source is proposed and experimentally investigated.Using the differential detecting magneto–optic rotation effect,a CPT spectrum with the background canceled and a high signal-to-noise ratio is obtained.The experimental results reveal that the sensitivity of the proposed scheme can be improved by half an order,and the ability to detect weak magnetic fields is extended one-fold.Therefore,the proposed scheme is suited to realize a pocket-size CPT magnetometer.

Melting phenomenon in magneto hydro-dynamics steady flow and heat transfer over a moving surface in the presence of thermal radiation

The Lie group method is applied to present an analysis of the magneto hydro-dynamics（MHD） steady laminar flow and the heat transfer from a warm laminar liquid flow to a melting moving surface in the presence of thermal radiation.By using the Lie group method,we have presented the transformation groups for the problem apart from the scaling group.The application of this method reduces the partial differential equations（PDEs） with their boundary conditions governing the flow and heat transfer to a system of nonlinear ordinary differential equations（ODEs） with appropriate boundary conditions.The resulting nonlinear system of ODEs is solved numerically using the implicit finite difference method（FDM）.The local skin-friction coefficients and the local Nusselt numbers for different physical parameters are presented in a table.

Technical Note and Brief Overview of the Materials Science and Technology along with Designing Aspects for Development of Spintronic Devices with Optimum Efficiency

One of the major challenges in designing and fabricating Spintronic devices is the choice of both, Materials and the Technology, along with understanding the intricacies of the Designing aspects. In this communication, we have attempted to briefly discuss these factors, with an aim to draw the attention of the Materials Scientists and Technologists to this serious challenge, in the direction of which, though a lot of research and development work has been done, still needs more concerted efforts to be made in order to make the Spintronic devices that can offer good efficiency for maximizing their usefulness.

Analysis of Magnetic Field and Torque for All-Harmonic-Torque Motor with Surface-Mounted Permanent Magnets

With the development of the advanced industrial products and technologies,the requirements for permanent magnet synchronous motors(PMSM)with high torque density are increasing.This paper proposed a new type of PMSM,named All-Harmonic-Torque PMSM(AHT-PMSM),which could use all harmonics of the magneto motive force(MMF)generated by permanent magnets and armature currents to enhance the electromagnetic torque.The stator windings structure,drive converter configurations and control model of the AHT-PMSM are illustrated firstly.And then the harmonic characteristics of the MMF generated by permanent magnets and armature currents are analyzed.It is found that the MMFs of permanent magnets and armature currents include the same order harmonics and each order harmonic is orthonormal for each other.Finally the calculation process of the average electromagnetic torque for AHT-PMSM based on harmonic MMFs is deduced.It is demonstrated that the theoretical average electromagnetic torque of AHT-PMSM is improved by 23%comparing to that of the normal sinusoidal PMSM when they are with the same structure sizes and armature MMFs.A 24-slot/4-pole AHT-PMSM and sinusoidal PMSM prototypes with the same sizes are modeled and manufactured,the comparison conclusion is validated by the finite element analyses(FEA)and experimental results.