Ku波段球体目标系的电磁复合散射研究

研究了球形目标之间的电磁相互作用,得到了目标二次散射场的表达式,给出了目标的复合散射场以及双站复合散射截面,并在Ku波段进行了数值仿真.结果表明：目标的尺寸对前向散射和后向散射均有较大的影响,周围目标的影响呈现出一定的周期性,二次散射随着目标间距的增大而减小,周围目标离前向散射方向越近,对前向散射的影响也越大.目标的二次散射场与一次散射场强度之比在10^-4数量级以上.在研究多粒子的相互影响时,周围的粒子可近似看作尺寸一定的粒子.利用所得结果以及坐标变换可以研究三维体系内粒子间的电磁相 关键词： 散射截面 二次电磁散射 电磁相互作用     

Investigation of Electromagnetic Complex Scattering for Spherical Targets in Ku Wave Band

This paper studies the electromagnetic reciprocity among spherical targets. The second scattering field for a target is derived in detail. The complex scattered field and the bistatic RCS are presented respectively. The simulations for the obtaining result in Ku wave band show that the size of the principal target affects greatly both the forward scatter and the backward scatter. The influence of the targets around shows definite periodicity. The second scattered field decrease with the increase of distance between two targets. The more near the forward area the rounding target is, the bigger its affect is. The magnitude of the second scattered field is about 10^–3 comparing with that of the first scattered field. The size of surrounding particles can be considered as a stated scale when researching the electromagnetic reciprocity. This kind of interaction for three dimensions can be investigated easy by using the obtained result and coordinate transformation.     

Electromagnetic scattering from a two dimensional perfect electromagnetic conductor (PEMC) strip and PEMC strip grating simulated by circular cylinders

Electromagnetic scattering of an incident plane wave from a rectangular strip and strip grating, are presented semi-analytically. The strip and strip grating are simulated by joining parallel perfect electromagnetic conductor (PEMC) circular cylinders and are illuminated by a TM_z incident plane wave. The PEMC medium does not allow electromagnetic energy to enter. An interface of this medium serves as an ideal boundary to the electromagnetic field. The solution is based on the application of the boundary conditions on the surface of each cylinder in terms of its local coordinate system. The technique is used to predict the scattered field pattern of PEMC strip and PEMC strip grating.     

Three-dimensional electromagnetic PIC model of a compact ECR plasmasource

A three-dimensional electromagnetic particle-in-cell (PIC) model is developed and used to model a compact ECR plasma source. The finite-difference time-domain (FDTD) technique is used to model the microwave fields which excite the plasma at 2.45 GHz. The PIC technique is used to model the dynamics of both the electrons and ions in the plasma. The grid structure used is constructed using the cylindrical coordinate system. Techniques which permit stable numerical solutions in the cylindrical coordinate system are developed and described. The electromagnetic fields and the plasma dynamics are solved in a self-consistent manner. A compact ECR (electron cyclotron resonance) plasma source used for the generation of ions for materials processing is simulated. This source has a plasma size of 3.6 cm in diameter and 3 cm in height. Simulation results of microwave power absorption, plasma potential, and microwave electric fields are presented. Distributed computing techniques are explored to handle the large computer memory requirements and the long computer simulation times associated with the three-dimensional particle-in-cell plasma model     

Investigation of the properties of the flux and interaction of ultrahigh-energy cosmic rays by the method of local-muon-density spectra

A new method for studying extensive air showers is considered. The method is based on the phenomenology of the localmuon density. It is shown that measurement ofmuon-density spectra at various zenith angles makes it possible to obtain information about the energy spectrum, mass composition, and interaction of cosmic rays over a broad range of energies (10¹⁵–10¹⁸ eV) by using a single array of comparatively small size. The results obtained from a comparison of experimental data on muon bundles from the DECOR coordinate detector with the results of simulation performed under various assumptions on the properties of the primary flux and for various hadron-interaction models are presented, and possible versions of the interpretation of these results are discussed.     

Tuneabilities of localized electromagnetic modes in random nanostructures for random lasing

The modal characteristics of localized electromagnetic waves inside random nanostructures are theoretically presented. It is crucial to know the tuneabilities of the localized modes systematically for demonstrating a specific random lasing application. By use of FDTD (Finite-Difference Time-Domain) method, we investigated the impulse response of two-dimensional random nanostructures consisting of closely packed cylindrical dielectric columns, and precisely analyzed the localized modes. We revealed the tuneability of the frequency of the localized modes by controlling the medium configurations: diameter, spatial density, and refractive index of the cylinders. Furthermore, it is found to be able to tune the Q (quality) factors of the localized modes dramatically by controlling simply the system size of the entire medium. The observed Q factors of approximately 1.6×10⁴ were exhibited in our random disordered structures.     

An experimentally validated electromagnetic energy harvester

A relatively simple method for determining the electromechanical parameters of electromagnetic energy harvesters are presented in this paper. The optimal power generated through a load resistor at both off-resonance and resonance is derived analytically. The experimentally measured performance of a rudimentary electromechanical energy harvester using a rare-earth magnet shows good agreement with the results from the model. The parasitic generator coil resistance can have a profound effect on the overall performance of an electromagnetic generator by essentially acting to degrade the effective coupling coefficient. Data from the setup electromagnetic generator shows normalized power densities of 1.7 μW/[(m/s²)² cm³] operating at a resonance frequency of 112.25 Hz. This power density is comparable with other electromagnetic devices of the same volume operating at these frequencies. The power output of the presented electromagnetic generator is comparable to equivalent piezoelectric generators.     

柱坐标系中截断光束的广义M2因子

推导出截断圆对称光束二阶矩的传输方程，它们与无截断光束的二阶矩满足相似的传输定律.因此，基于广义截断二阶矩方法，将直角坐标系中截断二维光束的二阶矩特征参数推广到柱坐标系中的截断圆对称光束，类似方法定义的广义M²因子（M²_G因子）是一个传输不变量.对理论的自洽性作了物理解释.推导出柱坐标系中截断超高斯光束的二阶矩参数和M²_G因子.对一些有意义的特殊情况作了讨论，并以数值计算例作了说明. 关键词： 光束描述 截断光束 圆对称性 广义截断二阶矩(GTSM) 2因子（M²_G因子）')" href="#">广义M²因子（M²_G因子）     

The electromagnetic two-body problem in special relativity

A system of two point charged particles is considered. Each particle moves in the electromagnetic field created by the other particle according to Maxwell's equations. A scheme of successive approximations is developed to study the field and the motion of the charges. The field (potentials and intensities) are exapanded in powers of c^?1 using a retarded time coordinate. The variables of the motion (position vectors, velocities, etc) are expanded in powers of c^?1 with coefficients depending on t only. The field is evaluated in the first three approximations. The equations of motion are derived in the same approximations and the corresponding conserved quantities are explicitly given. Thus, the usual assumption of an action-at-a-distance principle is avoided and the original nonlinear integrodifferential equations are reduced to a sequence of linear equations.     

The interpretation of the C metric. The charged case whene 2 ≤m 2

The charged C metric involves three parametersm, e andA representing mass, charge and acceleration respectively. Using a method developed in a previous paper, we show that whene ² m ² the metric may be interpreted in terms of two Reissner-Nordström particles, each of massm and with charges +e and –e, in accelerated motion and connected by a spring. The method depends on the fact that for certain regions of the coordinate space the charged C metric may be transformed into the Weyl form for a static axisymmetric system. In this form the horizons of the C metric become line sources. One of the regions leads to a Weyl metric with two line sources, one of finite length which corresponds to the outer horizon of a Reissner-Nordström particle and the other semi-infinite corresponding to a horizon associated with uniform accelerated motion. A further coordinate transformation leads to a metric valid for a larger region of space-time in which there are two charged particles in accelerated motion. WhenAm is small, the electromagnetic invariants approximate to those for the Born field for two accelerated charges in special relativity.     

Analytical solutions of transient pulsed eddy current problem due to elliptical electromagnetic concentrative coils

The electromagnetic concentrative coils are indispensable in the functional magnetic stimulation and have potential applications in nondestructive testing.In this paper,we propose a figure-8-shaped coil being composed of two arbitrary oblique elliptical coils,which can change the electromagnetic concentrative region and the magnitude of eddy current density by changing the elliptical shape and/or spread angle between two elliptical coils.Pulsed current is usually the excitation source in the functional magnetic stimulation,so in this paper we derive the analytical solutions of transient pulsed eddy current field in the time domain due to the elliptical concentrative coil placed in an arbitrary position over a half-infinite plane conductor by making use of the scale-transformation,the Laplace transform and the Fourier transform are used in our derivation.Calculation results of field distributions produced by the figure-8-shaped elliptical coil show some behaviours as follows:1) the eddy currents are focused on the conductor under the geometric symmetric centre of figure-8-shaped coil;2) the greater the scale factor of ellipse is,the higher the eddy current density is and the wider the concentrative area of eddy current along y axis is;3) the maximum magnitude of eddy current density increases with the increase of spread angle.When spread angle is 180,there are two additional reverse concentrative areas on both sides of x axis.     

Stationary Electromagnetic Fields of a Slowly Rotating Magnetized Neutron Star in General Relativity

Following the general formalism presented by Rezzolla, Ahmedov and Miller, ⁽¹⁾ we here derive analytic solutions of the electromagnetic fields equations in the internal and external background spacetime of a slowly rotating highly conducting magnetized neutron star. The star is assumed to be isolated and in vacuum, with a dipolar magnetic field not aligned with the axis of rotation. Our results indicate that the electromagnetic fields of a slowly rotating neutron star are modified by general relativistic effects arising from both the monopolar and the dipolar parts of the gravitational field. The results presented here differ from the ones discussed by Rezzolla, Ahmedov and Miller ⁽¹⁾ mainly in that we here consider the interior magnetic field to be dipolar with the same radial dependence as the external one. While this assumption might not be a realistic one, it should be seen as the application of our formalism to a case often discussed in the literature.     

The electromagnetic energy and momentum of finite charged bodies moving at constant velocity

It is shown that a purely electromagnetic, divergence-free tensorS ^ij , can be defined for any electrically charged body which is held in equilibrium by some cohesive force and moving at some constant velocity. This tensor appears to represent the electromagnetic energy-momentum of the body; the integral (1/c) ∝S ^ij dS _j (dS _j is the differential element of any spacelike hypersurface) iscM ₀ μ ⁱ the electromagnetic four-momentum of the system (M ₀ is the electromagnetic rest mass of the system,U _i is the four-velocity). The divergence-free property ofS ^ij depends only on Maxwell's equation and the condition of uniform motion. It is suggested that whatever the nature of the cohesive forces within such a system the total stress-energy tensor will, in effect, break up into two parts which are separately divergence-free: the purely electromagnetic tensor,S ^ij , and a tensor representing the energy-momentum of the cohesive forces. Just as it makes sense to speak of the electromagnetic mass of a system at rest without regard to the cohesive forces, it makes sense to talk about the electromagnetic momentum of the system, when it is moving at constant velocity, without reference to the cohesive forces.     

狭窄波束型高频引力辐射与电磁场的作用效应

从弱引力场的Einstein-Maxwell方程出发,讨论了晶体空间阵列的狭窄波束型高频引力辐射与电磁场的作用效应,并给出了扰动解。计算表明,在TT(Transvese Traceless)坐标系中,最优辐射方向的引力波束是纯十型极化的,并可使同频的电磁波产生倍频的扰动效应,使静态电磁场产生与时间成线性关系的累积扰动效应。对于任意方向上的引力辐射波束,在垂直于引力波矢的平面内仍然是纯十型极化的。在高频辐射和实验室典型尺度条件下,TT坐标系与Fermi坐标系的差异是可以忽略的。 关键词：     

轨道炮速度趋肤效应的分析与仿真

 根据Maxwell方程推导出电磁场参数与速度之间的关系,建立了直角坐标下的电磁场和温度场扩散2维偏微分方程, 分析了固体电枢电磁轨道炮的速度趋肤效应。以矩形固体电枢为例,给出了边界条件和激励源函数。采用有限差分法对方程进行求解,并对数据进行了分析,得到轨道和电枢中磁感应强度、温度和电流密度的分布曲线。计算结果表明:电枢的运动使得电流密度集中在电枢和轨道交界面的尾部,使得该局部地区温度增加,进而引起电枢尾部的熔融与烧蚀。     

Long-range potentials and the electromagnetic polarizabilities

The long-range spin and velocity independent forces of electromagnetic origin which act between any two systems are studied for those cases in which no forces of this type exist to order e². It is shown that they are uniquely determined by the charge, magnetic moment, and polarizabilities of both systems, not only to the dominant order r^?n, but also to the next one r^?(n+1). These potentials provide the link between Compton scattering polarizabilities (response to real photons) and classically defined polarizabilities (response to static electromagnetic field). The two definitions are shown to be equivalent for neutral spinless systems; the problems arising for a neutral particle with magnetic moment are studied in detail. The r^?(n+1) terms have no classical counterpart, since they are due to the relativistic quantum propagation of the system which carries charge or magnetic moment. The results are of general validity with analyticity, crossing, unitarity, and gauge invariance as only inputs. The most general conclusion is that the polarizabilities represent electromagnetic properties of a system at order e², as the charge and magnetic moment do at order e. Thus they give the strength of the response to electric and magnetic fields, independently of the specific characteristics of the electromagnetic agent.     

双星放射引力辐射的阻尼力

本文计算了双星的辐射阻尼。按照广义相对论,在广义坐标变换下,星体的运动方程中出现的力是与坐标的选择有关的。不同坐标条件将原则上导致不同的阻尼力。现在人们已经成功地观察到双星辐射阻尼效应。这表明应该找出一个物理的坐标系。在这个坐标系中算出的阻尼力等于观察到的值。我们提出下面物理条件代替通常的坐标条件。这个条件就是不存在时间方向和纵向极化的引力波。这个条件在所要求的近似下决定了我们认为是物理的坐标系。在这个坐标系中得出双星公转周期p的变化为P=-6.5×10^-12(m₁m₂)/M_⊙²((m₁+m₂)/m_⊙)^-1/3。 关键词：     

Analytical Formulation for ϕ 4 Field Potential Dynamics

An analytical model for adding a space-dependent potential to the ? ⁴ field equation of motion is presented, by constructing a collective coordinate system for the solitary solutions of this model. The interaction of ? ⁴ solitons with a delta function potential barrier and also delta function potential well is investigated. Most of the characters of interaction are derived analytically while they are calculated by other models numerically. We will find that the behaviour of a solitary solution is like a point particle which is moved under the influence of a complicated effective potential. The effective potential is a function of the field initial conditions and also of parameters of the added potential.     

Electrodynamics in accelerated frames revisited

Maxwell's equations are formulated in arbitrary moving frames by means of tetrad fields, which are interpreted as reference frames adapted to observers in space‐time. We assume the existence of a general distribution of charges and currents in an inertial frame. Tetrad fields are used to project the electromagnetic fields and sources on accelerated frames. The purpose is to study several configurations of fields and observers that in the literature are understood as paradoxes. For instance, are the two situations, (i) an accelerated charge in an inertial frame, and (ii) a charge at rest in an inertial frame described from the perspective of an accelerated frame, physically equivalent? Is the electromagnetic radiation the same in both frames? Normally in the analysis of these paradoxes the electromagnetic fields are transformed to (uniformly) accelerated frames by means of a coordinate transformation of the Faraday tensor. In the present approach coordinate and frame transformations are disentangled, and the electromagnetic field in the accelerated frame is obtained through a frame (local Lorentz) transformation. Consequently the fields in the inertial and accelerated frames are described in the same coordinate system. This feature allows the investigation of paradoxes such as the one mentioned above.     

A generalized approach to the calculation of ro-vibrational spectra of triatomic molecules

A generalization of the well known atom-diatom scattering hamiltonian to a coordinate system of two lengths and an angle is derived, another special case of which is a previously known bond angle-bond length hamiltonian. Different axis embeddings are also considered. The formalism is applied to the ro-vibrational levels of D₂H⁺, CH⁺ ₂ and HDHe (A ¹ A′) and the advantage of a judicious choice of coordinates demonstrated. The vibrational band origins for HDHe*, the first predictions for this system for which previous calculations had failed, are obtained using a new geometrically defined coordinate system. It is suggested that these coordinates might be used to represent isotopically substituted van der Waals complexes.