An Isolated Sensor Determining the Poynting Vector in the near Field of a Radiating Antenna

A system is described comprising of an isolated sensor to measure the polarization ellipses of the electric and magnetic vectors in the near field around a transmitting antenna or a scatterer in the frequency range from 0.5 to 10 MHz. The locus of the time-dependent Poynting vector is derived by numerical calculation. Results are displayed as a stereoscopic image.     

均匀场聚焦带状注速调管电子光学系统的研究

本文系统地阐述了均匀场聚焦带状电子注的传输理论,设计了柱面阴极皮尔斯电子枪,模拟显示轨迹的层流性较好;设计了产生均匀磁场的磁聚焦结构,在1 m长的距离内,成功地实现了X波段100 MW带状电子注的稳定传输,电子注通过率达到100%;同时设计了收集极新型结构,给出了电子注在收集极内的发散情况。     

Nonreciprocal transmission spectrum of a ferrite plate-resonant element grating metasandwich with split resonance

It is established that, when microwaves propagate in a structure comprising a ferrite plate and a grating of conducting resonant elements (situated on or close to the plate), the nonreciprocal wave transmission is accompanied by a nonreciprocal splitting of the microwave resonance at the grating frequency and by an expansion of the resonance bandwidth upon application of a constant magnetic field with a magnitude about one order smaller than that of the field exciting the ferromagnetic resonance (FMR). The sign of the nonreciprocity changes when the ferrite is arranged on the opposite side of the grating and/or when the applied constant magnetic field reaches a level at which the difference between the FMR and the grating resonance frequencies changes sign.     

Giant nonreciprocal effect under conditions of mutual influence of ferromagnetic and chiral resonances

A more than hundredfold increase in the nonreciprocity of electromagnetic wave transmission in a waveguide containing a transversely magnetized ferrite plate has been observed upon the introduction of a grating of bianisotropic elements. This effect takes place at a certain magnitude of a constant magnetic field, under the conditions of mutual influence of ferromagnetic and chiral resonances. In an evanescent regime, the non-reciprocity exhibits a severalfold increase. The effect depends on the mode of excitation of the chiral resonance, being observed in the case of excitation by a magnetic component of the microwave field.     

Magnetooptical interference effects in a structure featuring a 2D electron gas

Magnetooptical effects in a system with a 2D electron gas are considered, which are related to the interference resonances appearing in a plane-parallel plate exposed to a weak magnetic field. A new method is proposed for contactless measurements of the Hall conductivity in a 2D electron system.     

Ordering of free-standing Co nanoparticles

Colloidal Co particles of 11 nm diameter were deposited on Si substrate by spin coating and/or casting in magnetic field. A perpendicular magnetic field varying along the diagonal of the substrate was also applied. The samples were analyzed by transmission electron microscopy (TEM), field emission gun scanning electron microscopy (SEM-FEG), atomic and magnetic force microscopy (AFM/MFM). TEM micrographs show local order when a Co nanoparticle monolayer is deposited on Si. Drying the colloidal solution in a magnetic field leads to the formation of quite large clusters (0.3 μm) of Co nanoparticles. A stripe structure was then observed when the particles were deposited by casting in the varying magnetic field. AFM/MFM measurements show isolated Co clusters on the stripes. Magnetic features corresponding to the single Co cluster have been observed pointing out that all magnetic moments in the cluster are oriented along the field direction.     

运用蒙特卡罗方法分析像增强器分辨率

介绍了运用蒙特卡罗方法分析三代微光像增强器分辨率的方法。该方法取一组随机数,来模拟像管中光电阴极受激发射的电子。综合考虑微通道板参数、第一近贴距、第二近贴距、阴极电压和荧光屏电压等影响,模拟追踪电子的运动轨迹。并根据像面上电子的落点分布来计算调制传递函数,从而确定像管的分辨率。经比较,此方法计算简单、运行快速,模拟结果与实验值的偏差不超过5%,理论模型满足实际需求,可为三代微光像增强器的设计提供参考。     

Axial particle trajectory measurements in high-gradient magnetic separation

A technique has been developed for studying the trajectories of paramagnetic particles in a high-gradient magnetic separator. Human red blood cells are used as the paramagnetic particle and their trajectories in relation to a single magnetized stainless-steel wire are imaged. The flow velocity is parallel to the wire and has a value of approximately 50 μm . s^-1. The magnetic field of 1.4 T is applied perpendicular to the wire. A phase modulation technique is used to image the red blood cells with a resolution of less than 0.5 μm. The measured particle trajectories confirm the main features of current theoretical models.     

Second-order hot image from a scatterer in high-power laser systems

A theory is developed for predicting a second-order hot-image formation in high-power laser systems. Light diffracted from a small optical scatterer interferes with an intense original wave in the nonlinear medium to produce a hologram like a Fresnel-zone plate. The theoretical model shows that the hologram produces a negative first-order diffractive wave focused to the traditional hot image and negative second-order diffraction that causes another intense image, namely, a second-order hot image. It is found by analysis that the location of the second-order hot image arises in a downstream plane with a half-distance from the medium to the scatterer. Results of the numerical calculations show that the peak intensity of the nonlinear image may reach a level high enough to damage optical components with the increase of the breakup integral (B integral), indicating that the image may also potentially damage expensive optical components in high-power laser systems.     

The principle of similarity of trajectories for the motion of charged particles with different masses in electric and magnetic fields that are homogeneous in Euler terms

An electric field with potentials that is homogeneous in Euler terms satisfies the principle of similarity of trajectories that was derived by Yu.K. Golikov. Such fields are a useful tool for the development of electron and ion optical systems with unique properties. In this paper, the principle of similarity of trajectories is generalized to the case of a magnetic field and a combined electric and magnetic field that are homogeneous in Euler terms.     

Template-free synthesis of nickel nanowires by magnetic field

Nickel nanowires were prepared by a template free method combined with chemical reduction and magnetic field. The application of an external magnetic field resulted in the formation of self-aligned metallic nickel nanowires of about 50 nm in diameter. Nickel particles were prepared in the absence of a magnetic field to better illustrate the structure directing role of the magnetic field. Physical properties of the nickel nanochains were examined by scanning electron microscopy (SEM), transmission electron microscope (TEM), X-Ray diffraction (XRD), and thermogravimetric analysis (TGA) methods. This study provides a simple method to prepare Ni nanowires in large scale which broads their practical applications.     

Chaotic oscillator with electron feedback and magnetic field at the cathode

The influence of a magnetic field at the cathode on the operation of a low-voltage vircator with electron feedback has been experimentally studied. It is shown that this magnetic field can significantly improve the characteristics and parameters of the vircator, provided that the field lines do not coincide with electron trajectories in the system.     

An integral equation method for the solution of 3-dimensional,non-linear,magnetostatic problems

A finite element method for computing the resultant magnetic field arising from a given source field in the presence of a magnetic material of variable permeability is described; in this method finite element approximations to the scalar potential of the resulting field and the magnetic susceptibility, in the region occupied by the magnetic material, are determined from the non-linear integral equation for the scalar potential and the constitutive susceptibility relation, using a collocation scheme. The method is used to compute the shielding effect of a thin rectangular plate of variable permeability on a given source field. The plate is subdivided uniformly into brick elements; the resulting translational invariance of the integrals required in the calculations is exploited to achieve major computational savings. A consequence of the thinness of the plate is that the calculation of the requisite integrals by analytic methods leads to considerable loss of accuracy by differencing; this difficulty is overcome by using a scheme which combines both analytic and quadrature techniques. The resulting system of non-linear algebraic equations is solved by Powell's hybrid method; an efficient scheme for calculating an initial approximation to the Jacobian, which utilizes the structure of the equations, is presented. The results of the calculations are discussed.     

Hall effects on magnetohydrodynamic free convection about a semi-infinite vertical flat plate

A theoretical analysis is presented for the problem of free convection flow of a conducting fluid along a semi-infinite vertical flat plate when the fluid is permeated by a transverse magnetic field and the Hall effects are taken into account. The derived fundamental equations on the assumption of small magnetic Reynolds number are solved numerically by employing the difference-differential method in combination with the Simpson's rule. The velocity and temperature profiles as well as the local Nusselt number are computed for various values of the Hall and magnetic parameters. The results are compared with those known from the literature.     

The micromagnetic propertis of high-coercivity metallic thin films and their effects on the limit of packing density in digital recording

The micromagnetic structures of the high-coercivity, isotropic, and high-squareness thin films of sputtered Co-Re have been investigated using transmission electron microscope (TEM) Lorentz imaging and electron deflection methods. From the behavior of the magnetic ripple structure under applied field and the configuration of the local surface fields observed in these experiments, the existence of magnetic clusters in these films was verified. Based on the interpretation of the field dependence of the ripple formation and the hysteretic properties of the film, it is concluded that the formation of the magnetic clusters is a spontaneous process resulting from intercrystalline interactions and local inhomogeneities in the anisotropy. The effects of such cluster formation on longitudinal magnetic recording were investigated. The results show that the reduction of dipole energy at the transition region between two oppositely magnetized regions can be achieved by a stepwise rotation of the magnetization vector of an individual cluster in the form of a vortex. This type of rotation creates a finite transition length which is limited by the size of the magnetic cluster of the film. Consequently, it is concluded that the maximum packing density for saturation recording in these types of films would be less than that predicted by the phenomenological equation, which was derived based solely on considerations of the demagnetization field and the coercivity of the film.     

The gain in the plane wiggler with inhomogeneous magnetic field

We calculate the gain in a plane wiggler (undulator) with inhomogeneous magnetic field and in the external electromagnetic wave. The electromagnetic field-induced corrections to electron trajectories are found. The linear (field-independent) gain is calculated using these corrections to complex motion of electrons, which was described in previous paper, without electromagnetic field. This complex motion arises because of magnetic field inhomogeneity. It is shown that the account of inhomogeneity of the magnetic field leads to appearance of additional peaks in the gain of usual wiggler with uniform magnetic field.     

A method to correct coordinate distortion in EBSD maps

Drift during electron backscatter diffraction mapping leads to coordinate distortions in resulting orientation maps, which affects, in some cases significantly, the accuracy of analysis. A method, thin plate spline, is introduced and tested to correct such coordinate distortions in the maps after the electron backscatter diffraction measurements. The accuracy of the correction as well as theoretical and practical aspects of using the thin plate spline method is discussed in detail. By comparing with other correction methods, it is shown that the thin plate spline method is most efficient to correct different local distortions in the electron backscatter diffraction maps.     

Dipole and solenoidal magnetic moments of electronic surface currents on toroidal nanostructures

The time-dependent Schr?dinger equation is developed for a spinless electron which is confined to move on a toroidal surface and curvature effects are taken into account. The electron motion is driven by linearly or circularly polarized microwaves including an interference field. To calculate the magnetic moments which are induced by the electronic surface currents on the torus an eight-state basis set is used. The system is driven at a resonance frequency to allow for transitions between states with opposite θ-parity. Optical transitions into modes of excitation can be observed that correspond to a magnetic dipole term parallel to the toroidal central symmetry axis as well as additional components in radial and azimuthal direction (solenoidal modes). Size and relative magnitude of the different components can be steered by adjusting magnitude, polarization, and phase information of the microwave field. Substantial enhancements of the solenoidal magnetic modes versus the dipole mode can be observed when adding a sufficiently strong static magnetic field parallel to the symmetry axis.      

Measurements of the field distribution in discontinuous metal films using transmission electron microscopy

The electric or magnetic field distribution in a discontinuous metal film is determined from a change of the image contrast observed in the transmission electron microscope. According to the estimates, this method can be used for measurement of electric fields larger than 10⁶ V m^-1 with a spatial resolution of a few ångströms.