旋转圆柱靶磁控溅射阴极的磁场模拟及结构设计

基于旋转圆柱靶磁控溅射阴极的工作原理,建立其结构模型,并应用ANSYS有限元方法对旋转靶阴极磁场进行了模拟计算,得到了磁场分量Bx在靶材表面上的二维磁场分布规律。通过调节磁铁的宽和高、磁铁间夹角以及设置可移动磁性挡板等方法优化磁场并设计了一种新型磁场结构旋转靶。本研究为旋转靶磁控溅射阴极的磁场结构设计提供了理论依据。     

Hybrid finite-element method for discretising cylindrically symmetric parts in electrotechnical models

In many technical devices such as transformers and electrical machines, large differences in geometric dimensions are observed. As a consequence, the generation of a 3D computational grid for the whole device leads to unacceptably large numbers of elements or can even fail. In addition to the commonly applied cartesian or cylindrical symmetries of the overall geometry, the model can be subdivided into parts featuring translational or cylindrical symmetries. Such parts are discretised separately, accounting for the local symmetry, and are then combined with the surrounding 3D model. Excitations and boundary conditions of the submodels are not necessarily symmetric but are expected to be smooth in the direction of the symmetry. Then, the field distribution at the interface is well approximated by a set of spectral elements along the dimension of symmetry. Coupling between the model parts is carried out by means of Lagrange multipliers. A single-phase transformer with thin insulation sheets is taken as an example to illustrate the proposed hybrid discretisation. The cross-section of the cylindrically symmetric part containing thin sheets, is represented by a fine 2D finite-element mesh so that all the geometrical details can be resolved, and the rest of the structure is discretised by a 3D mesh. Nevertheless, a fully 3D field distribution is calculated in all model parts. Only a small number of harmonic functions is needed to account for the azimuthal field variation at the cylindrical interface. Hence, the number of unknowns in the numerical model is reduced significantly, while a high level of accuracy is maintained     

3D elastic wave propagation modelling in the presence of 2D fluid-filled thin inclusions

In this paper, the traction boundary element method (TBEM) and the boundary element method (BEM), formulated in the frequency domain, are combined so as to evaluate the 3D scattered wave field generated by 2D fluid-filled thin inclusions. This model overcomes the thin-body difficulty posed when the classical BEM is applied. The inclusion may exhibit arbitrary geometry and orientation, and may have null thickness. The singular and hypersingular integrals that appear during the model's implementation are computed analytically, which overcomes one of the drawbacks of this formulation. Different source types such as plane, cylindrical and spherical sources, may excite the medium. The results provided by the proposed model are verified against responses provided by analytical models derived for a cylindrical circular fluid-filled borehole.The performance of the proposed model is illustrated by solving the cases of a flat fluid-filled fracture with small thickness and a fluid-filled S-shaped inclusion, modelled with both small and null thickness, all of which are buried in an unbounded elastic medium. Time and frequency responses are presented when spherical pulses with a Ricker wavelet time evolution strikes the cracked medium. To avoid the aliasing phenomena in the time domain, complex frequencies are used. The effect of these complex frequencies is removed by rescaling the time responses obtained by first applying an inverse Fourier transformation to the frequency domain computations. The numerical results are analysed and a selection of snapshots from different computer animations is given. This makes it possible to understand the time evolution of the wave propagation around and through the fluid-filled inclusion.     

Electrical transport and magnetoresistance in La2/3Sr1/3MnO3 polycrystalline composite thin films

The manganite La_2/3Sr_1/3MnO₃ (LSMO)/CuO and LSMO/Al₂O₃ polycrystalline composite thin films are deposited on Si (111) substrates in a magnetron sputtering system, using the tandem deposition method. The electrical transport and magnetoresistance properties of the films have been systematically investigated. By considering two parallel conduction channels at the grain boundary, we obtain a general expression for the temperature dependency of the resistance that agrees with the experimental data measured in LSMO polycrystalline composite thin films at whole temperature region of 300 K-10 K under the condition of zero magnetic field. Also, the resistance vs. temperature curve under an external magnetic field can be obtained by only varying one parameter in the model. It provides an effective way to obtain the high-temperature grain boundary magnetoresistance in the polycrystalline manganite.     

A 3-D Magnetic Charge Finite-Element Model of an Electrodynamic Wheel

When a magnetic rotor is both rotated and translationally moved above a conductive, nonmagnetic, guideway eddy currents are induced that can simultaneously create lift, thrust, and lateral forces. In order to model these forces, a 3D finite-element model with a magnetic charge boundary has been created. The modeling of the rotational motion of magnets by using a fictitious complex magnetic charge boundary enables fast and accurate steady-state techniques to be used. The conductive regions have been modeled using the magnetic vector potential and nonconducting with the magnetic scalar potential. The steady-state model has been validated by comparing it with a Magsoft Flux 3D transient model (without translational velocity) and with experimental results. The 3D model is also compared with a previously presented 2D steady-state complex current sheet model.     

The hydrodynamic theory of a positive discharge column in an axial magnetic field

The influence of an axial magnetic field on the performance of a low-pressure cylindrical positive discharge column is studied from the hydrodynamic point of view. It is shown that the magnetic field affects the distribution of the plasma density, its speed, and the energy of electrons. The energy of electrons, the concentration and the speed of plasma, and the azimuth speed of electrons and ions as functions of the radius have been found for a helium atom in a magnetic field of varying intensity. It has been noticed that the electron and ion azimuth movement equations should account for inertia. The obtained hydrodynamic results significantly deviate from the ones obtained in the wide-spread diffusion model of a positive column. It is shown that the distribution of plasma concentration and the radial speed in the positive column are generally close to the results using the diffusion approach, if the axial inductance of the magnetic field and the gas density are increased. However, major differences are found near the walls.     

Quantum Theory of Spin Wave Gap in Ultrathin Magnetic Films

A simple quantum model is presented for the spin wave energy gap in single-layer and thin magnetic films that include both the magnetic out-of-plane and in-plane anisotropies. The films are assumed to be under the influence of the out-of-plane direction of the applied magnetic field at zero temperature. The calculated equations present a nonzero spin wave gap at zero magnetic field which is strongly affected by anisotropies. The effects of the film thickness and the role of the applied field are also examined. We discuss the results in connection with experimental data reported for nanocrystalline amorphous CoFeB films with growth-induced anisotropy.     

Effective optical properties of highly ordered mesoporous thin films

This paper expands our previous numerical studies predicting the optical properties of highly ordered mesoporous thin films from two-dimensional (2D) nanostructures with cylindrical pores to three-dimensional (3D) structures with spherical pores. Simple, face centered, and body centered cubic lattices of spherical pores and hexagonal lattice of cylindrical pores were considered along with various pore diameters and porosities. The transmittance and reflectance were numerically computed by solving 3D Maxwell's equations for transverse electric and transverse magnetic polarized waves normally incident on the mesoporous thin films. The effective optical properties of the films were determined by an inverse method. Reflectance of 3D cubic mesoporous thin films was found to be independent of polarization, pore diameter, and film morphology and depended only on film thickness and porosity. By contrast, reflectance of 2D hexagonal mesoporous films with cylindrical pores depended on pore shape and polarization. The unpolarized reflectance of 2D hexagonal mesoporous films with cylindrical pores was identical to that of 3D cubic mesoporous films with the same porosity and thickness. The effective refractive and absorption indices of 3D films show good agreement with predictions by the 3D Maxwell-Garnett and nonsymmetric Bruggeman effective medium approximations, respectively.     

3D Modeling Permanent Magnet Guideway for High Temperature Superconducting Maglev Vehicle Application

A three-dimensional analytical method is proposed to model the permanent magnet guideway (PMG) involved in the high-temperature superconducting (HTS) maglev vehicle system, and with this analytical method, the non-uniformity of magnetic field along the longitudinal direction of the PMG due to the existent gap between the adjacent permanent magnet (PM) can be taken into account in the simulation of the HTS maglev vehicle system. The analytical expressions for two rectangular PM with different magnetization directions are deduced from the Biot–Savart’s law. The 3D modeling of the PMG is validated from the four aspects, i.e., the comparison of the measurement and calculation value of the magnetic field; the magnetic field contour of the PMG; the comparison of the 3D method results with the 2D method; and the comparison of the results from the present 3D analytical model and previous finite element software. Currently, using the 3D analytical model, we have proposed a 3D method to numerically investigate the HTS magnetic levitation/suspension system with bulk high-temperature superconductor (HTSC).     

Finite element calculation of 4-step 3-dimensional braided composite under ballistic perforation

The ballistic perforation test results of 4-step 3-dimensional (3D) braided Twaron^®/epoxy composites, which were subjected to impact by conically cylindrical steel projectile, are presented. The residual velocities of projectile perforated composites target at various strike velocities were measured and also compared with that from finite element calculation. ‘Fiber inclination model’ for 3D textile composites was adopted to decompose the 3D braided composite at quasi-microstructure level for the geometrical modeling in preprocessor of FEM. The material modeling was also based on this simplified model. The finite element code of Ls-Dyna was used to simulate the impact interaction between projectile and inclined lamina. The residual velocity of projectile perforating the entire 3D braided composite can be calculated from the sum of kinetic energy loss of the projectile that obtained from FEM. From the simulation of ballistic penetration process and comparison between numerical results and experimental results, it proves that the analysis scheme of quasi-microstructure level in this paper is valid and reasonable. The simplified method in this paper could be extended to model other kinds of 3D textile composites under ballistic impact.     

NMR study of the effect of flow on3He-B

We have used a plastic diaphragm to generate flow in superfluid³HeB, through a cylindrical geometry, whilst monitoring the transverse NMR frequency. It was found that the critical flow velocity needed to induce NMR frequency shifts was dependent on the magnetic field. The results are explained by a numerical calculation of the texture in the³HeB, under the influences of magnetic field, fluid flow and surface energy terms. Also presented are measurements of the B phase NMR longitudinal frequency, derived from the magnitude of the flow-induced change in the transverse frequency. A flow-induced texture transition, which caused a dramatic narrowing of the NMR lineshape, is described.     

Nanoreinforced polymer composites: 3D FEM modeling with effective interface concept

A computational study of the effect of structures of nanocomposites on their elastic properties is presented. The special program code for the automatic generation of 3D multiparticle unit cells with/without overlapping, effective interface layers around particles is developed for nanocomposite modeling. The generalized effective interface model, with two layers of different stiffnesses and the option of overlapping layers is developed here. The effects of the effective interface properties, particle sizes, particle shapes (spherical, cylindrical, ellipsoidal and disc-shaped) and volume fraction of nanoreinforcement on the mechanical properties of nanocomposites are studied in numerical experiments. The higher degree of particle clustering leads to lower Young’s modules of the nanocomposites. The shape of nanoparticles has a strong effect on the elastic properties of the nanocomposites. The most effective reinforcement is cylindrical one, followed by ellipsoids, discs, and last, spheres. Ideally random oriented and correlated microstructures lead to the same average Young moduli, yet, the standard deviation of Young modulus for correlated microstructure is nearly 4 times of that for fully random orientation case.     

脉冲磁场激励下圆柱导体内瞬态涡流场的快速计算

建立了脉冲磁场激励下圆柱导体内瞬态涡流场的理论模型。实现了瞬态涡流场的快速计算。通过实例表明上述圆柱导体内瞬态涡流场的快速计算方法有效。     

Design and characterization of a theta-pinch imploding thin film plasma source for atomic emission spectrochemical analysis

A new atomization device for direct atomic spectrochemical analysis has been developed that uses the theta-pinch configuration to generate a pulsed, high-energy-density plasma at atmospheric pressure. Energy from a 20-kV, 6.05-μF capacitive electrical discharge was inductively coupled to a sacrificial aluminum thin film to produce a cylindrical plasma. Current waveform analysis indicates an average power dissipation of 0.5 MW in the plasma. Electromagnetic modeling studies were used to identify theta-pinch designs possessing characteristics favorable to both plasma initiation and plasma heating. The discharge was most robust when the induced current and rate of magnetic field change were maximized. Minimizing the ratio of the coil's width to its radius was also critical. Counter to intuition, a larger diameter was found to be more successful. Spectroscopic studies indicate that the discharge forms a heterogeneous plasma with a dense, cylindrical plasma sheet confined by the walls of the discharge tube surrounding a less energetic plasma in the center. Al(II) emission in the outer plasma cylinder was temporally aligned with the induced current whereas in the center it aligns with the magnetic field. Ionization of support gas species (Ar, He, and air) was not observed, although the identity of the gas had a significant influence on the plasma reproducibility. The optimized design utilized a 5.5-turn, 19-mm-diameter theta coil with argon as the support gas. Sb(I) emission from an antimony oxide solid powder sample deposited on the thin film was observed primarily in the outer part of the plasma. Analyte emission shows contributions from magnetic compression early in the discharge and from the induced current late in the discharge. The discharge produced analytically useful signals from solid antimony oxide samples. Using spatially and temporally resolved detection, the line-to-background ratio for Sb(I) was found to be greater than 4 for emission integrated from 55 to 120 μs.     

Anisotropice superfluid fraction of3He A1 phase

The superfluid fraction of³He a₁ phase is computed from measurements of the velocity of spin/entropy waves induced in a cylindrical chamber, for two different directions of the magnetic field: parallel and perpendicular to the axis of the chamber. The ratio of the superfluid fractions in the parallel and perpendicular orientations is 1.85, and does not depend on the field between 1 and 5 Tesla. We adapt a theoretical texture model to account for the superfluid flow, and the results are consistent with the above ratio and direct estimates of superfluid velocity.     

3D Fabrication of Fully Iron Magnetic Microrobots

Biocompatibility and high responsiveness to magnetic fields are fundamental requisites to translate magnetic small‐scale robots into clinical applications. The magnetic element iron exhibits the highest saturation magnetization and magnetic susceptibility while exhibiting excellent biocompatibility characteristics. Here, a process to reliably fabricate iron microrobots by means of template‐assisted electrodeposition in 3D‐printed micromolds is presented. The 3D molds are fabricated using a modified two‐photon absorption configuration, which overcomes previous limitations such as the use of transparent substrates, low writing speeds, and limited depth of field. By optimizing the geometrical parameters of the 3D molds, metallic structures with complex features can be fabricated. Fe microrollers and microswimmers are realized that demonstrate motion at ≈20 body lengths per second, perform 3D motion in viscous environments, and overcome higher flow velocities than those of “conventional 3D printed helical microswimmers.” The cytotoxicity of these microrobots is assessed by culturing them with human colorectal cancer (HCT116) cells for four days, demonstrating their good biocompatibility characteristics. Finally, preliminary results regarding the degradation of iron structures in simulated gastric acid liquid are provided.     

磁场中圆柱壳体的轴对称振动

导出了磁场中圆柱薄壳体的磁弹性轴对称振动方程及电磁力和力矩的具体表达式,并分别推得了壳体位子纵向和横向磁场中振动的特征方程。通过算例给出了振动频率和衰减系数随场强的变化曲线,表明适当磁场的通入,可达到控制壳体振动特性的目的。     

The effect of external cusp magnetic field on Ar ICP characteristics

In this paper, three permanent magnet rings, which were placed alternatively between the three antenna coils of a cylindrical inductively coupled radio frequency (rf) argon plasma for rf enhanced ionized magnetron sputtering system, were used to produce a closed magnetic field distribution with the magnetic field of the unbalanced magnetron sputtering to confine discharge plasma. Langmuir probe measurement was used to study the effect of the magnetic field on the plasma characteristics and their spatial distribution. The results show that the presence of the closed magnetic field leads to the increase of the ion density and the decrease of electron temperature and plasma potential. With the closed magnetic field, the plasma density distribution in radial direction will become more uniform.     

A semi-analytical finite element model for the analysis of cylindrical shells made of functionally graded materials

In the present work, a study of free vibrations of functionally graded cylindrical shells made up of isotropic properties is carried out. A semi-analytical axisymmetric finite element model using the 3D linear elastic theory is developed. The 3D equations of motion are reduced to 2D by expanding the displacement field in Fourier series in the circumferential direction, involving circumferential harmonics. The material properties are graded in the thickness direction according to a power law. The model has been verified with simple benchmark problems and the results show that the frequency characteristics are found to be close to published results of isotropic cylindrical shells. New results are included for FGM shells.