Time-Domain Analysis of Millimeter Wave Circulation Around a Magnetised Ferrite Sphere

An efficient numerical method has been devised for the study of wave circulated by a magnetised ferrite sphere. It is a finite-difference time-domain formulation that incorporates Mur's absorbing boundary conditions and a perfectly matched layer. The electromagnetic fields inside the ferrite body are calculated using special updating equations derived from the equation of motion of the magnetization vector and Maxwell's curl equations in consistency. The electromagnetic fields inside ferrite and the power-density distribution on the ferrite's surface normal to the bias external magnetic field are obtained in a wide frequency band with a single time domain run. It is observed that an incident plane wave would circulate around the magnetised ferrite body in an open space as if the ferrite were placed inside a waveguide / microstrip junction circulators.     

导体球涂覆各向异性铁氧体介质电磁散射的解析解

该文用球矢量波函数对各向异性铁氧体介质涂覆导体球的电磁散射解析解开展研究。各向异性铁氧体介质中电磁场的球矢量波函数解可表示成第一、二、三、四类球矢量波函数之和。根据球Bessel函数的性质,可以得出导体球涂覆各向异性铁氧体介质的球矢量波函数解析解。应用铁氧体与自由空间分界面上电磁场切向连续和在导体球面上切向电场等于零的边界条件以及球矢量波函数切向正交性质,可分别得出铁氧体介质中电磁场和散射场的展开系数。给出了平面波入射情况下的数值计算结果。该文的结果可应用于有关微波器件、天线以及目标特征的分析和计算。     

Characteristics of the electromagnetic radiation resulting from arbitrarily directed propagation of magnetostatic surface waves in an increasing transverse magnetic field

Radiation of the electromagnetic waves accompanying propagation of a magnetostatic surface wave with nonparallel directions of the phase and group velocities in a ferrite slab magnetized in its plane by a transverse linearly increasing magnetic field is analyzed using the model of accelerated motion of magnetic charges. It is shown that, at each point of the space surrounding the ferrite slab, the shape of the radiation pattern strongly depends on the angle between the direction perpendicular to the direction of propagation of the magnetic field and the direction of the wave vector of the magnetostatic surface wave.     

FDTD Analysis of EW Wave Circulating by a Magnetized Ferrite Body in Free Space

An efficient numerical method has been devised for the study of wave circulating by a magnetised ferrite body of an arbitrary shape. It is a finite-difference time-domain formulation that incorporates Mur's absorbing boundary conditions and a perfectly matched layer. Several shapes of interest have been studied, including spheres, circular cylinders. The electromagnetic fields inside ferrite and the power-density distribution on the ferrite's surface normal to the bias external magnetic field are obtained. It is observed that an incident plane wave would circulate around the magnetised ferrite body in an open space as if the ferrite were placed inside a waveguide junction circulator.     

Wave diffraction by a finite set of azimuthally magnetized ferrite cylinders

The article is devoted to the problem of scattering of plane linear and circular electromagnetic waves by a set of ferrite-coated cylinders. Particular attention is paid to the possibility of controlling the scattering pattern by the azimuthal magnetic field induced in the ferrite by the dc current in metal core of cylinders. It is shown that the best sensitivity can be obtained for the magnetic field, which provides the magnetic resonance inside ferrite layer. Relevant scattering patterns are also presented.     

The effect of the base composition and microstructure of nickel-zinc ferrites on the level of absorption of electromagnetic radiation

Promising absorbing materials include Ni—Zn ferrites, as they quite intensively absorb electromagnetic waves in the frequency range from 50 to 1000 MHz. The electromagnetic properties of Ni—Zn ferrite absorbing materials obtained by different technological methods were studied in this paper. A model making it possible to evaluate the dielectric permeability of the ferrite material, depending on the microstructure parameters and electrophysical properties of grain boundaries, was proposed. The influence of base composition and microstructure on the amount of absorption of electromagnetic radiation by Ni—Zn ferrite absorbing materials was determined. It was stated that the increase of the content of excess Fe₂O₃ to 51.0 mol % leads to the shift of the frequency range of the absorption of electromagnetic radiation towards lower frequencies. It can be explained by the increase of the dielectric and magnetic permeability of ferrite. Moreover, the introduction of an excess of Fe₂O₃ in the grinding stage of the synthesized burden is more efficient. It was revealed that increasing the sintering temperature to 1350°C also shifts the frequency range of absorption of electromagnetic radiation towards lower frequencies. Probably it is caused by the increase of the dielectric and magnetic permeability of ferrite and the shift of the resonance frequency of domain walls as a result of the formation of a coarse-grained structure.     

表面波放电狭缝天线辐射电磁场的三维数值分析

针对平板型表面波放电等离子体源,建立了表面波放电狭缝天线辐射电磁波模型,对狭缝天线辐射电磁场分布进行了三维数值计算,并与表面波电磁场进行对比分析,讨论了平板型表面波放电机理。结果表明:整个狭缝天线阵激发的电磁场是每个狭缝天线激发电磁场的线性叠加;狭缝天线阵直接激发的电磁场强度在临近波导壁面处很大,并且随着空间距离的增大迅速衰减;狭缝天线阵直接激发和表面波的电场均远大于各自的磁场,分析电、磁场对带电粒子的力作用时可以忽略磁场力的作用;表面波电磁场远大于狭缝天线阵直接辐射的电磁场,强电磁场范围也远大于狭缝天线阵直接激发的强电磁场范围,等离子体有增强电磁场强度、扩大强电磁场范围的作用。     

Theory of Operation of a 3-Port Y-Junction Ferrite Circulator

An analysis is made of the operation of a 3 port Y-junction ferrite circulator wherein it is assumed that the ferrite cylinder can support the propagation of a bound surface wave. The incident wave guided by the air-dielectric interface of the ferrite cylinder is taken to be linearly polarized parallel to the ferrite axis and after incidence on the cylinder is assumed to divide and propagate in opposite directions about the cylinder as two linearly polarized signals. By appropriate selection of ferrite cylinder diameter, permeability, magnetizing field and saturation magnetization, constructive and destructive interference of the RF components are shown to occur at the two output ports. The conditions for reinforcement and null at the outputs are discussed and compared with published experimental data. It is possible to predict the occurrence of ferrite circulator diplexing reported by Brown and Clark although good quantitative comparison is lacking. The theoretical dependence of ferrite diameter upon free space wavelength is computed and compares satisfactorily with recorded experimental data. The experimental observations that greater circulator bandwidths are achievable when below resonance magnetizing fields are employed are shown to have a theoretical basis. In addition, interrelationships among the designed variables: saturation magnetization, applied magnetic field, ferrite resonance linewidth and circulator insertion loss are noted in the theoretical results.     

Frequency series expansion of an explicit solution for a dipoleinside a conducting sphere at low frequency

The electromagnetic field generated by a current dipole situated at an arbitrary position inside a conducting sphere is derived using the expansions of the spherical vector wave functions. The first few terms in a series expansion of this field with respect to the frequency are given for the normal magnetic field (used in magnetoencephalogram) and the tangential electric field (used in electroencephalogram) outside the conducting sphere at low frequency. It is shown that the first correction term to the static solution is linear in the frequency ω (the second correction term is proportional to ω^3/2 ) and, thus, the static solution can be used as a good approximation for the solution at a very low frequency     

Electrophysical properties of composites with carbon nanotubes,fine graphite,and feritte microparticles as inclusions

The electrophysical properties of composites based on epoxy adhesive with inclusions in the form of carbon nanotubes, particles of fine-dispersed graphite, and ferrite microparticles have been investigated in the frequency range from 0.1 up to 6 GHz. The effect of the spatial arrangement of ferrite inclusions in the composite volume on the frequency of the transmission coefficient of microstrip photonic crystals has been shown. Magnitudes of transmittance and reflection in the window of transparency of a photonic crystal has been established to be determined by the spatial arrangement of the ordered ferrite inclusions (ferrite filaments) relative to the direction of an electric field vector of an electromagnetic wave and its direction of propagation the photonic crystal. It has been found that with an increase in the induction value of the orienting magnetic field acting during an epoxy cure, the distance between the regularly arranged inclusions of ferrite (ferrite filaments) decreases.     

The structure of high-frequency fields of a surface spin wave in a tangentially magnetized ferrite plate

Vector lines of the high-frequency magnetic field, magnetic induction, and magnetization of a surface spin wave in a tangentially magnetized ferrite plate are calculated. It is found that the magnetic induction vector lines form contrariwise directed curls that are localized near the opposite surfaces of the plate. It is shown that the structure of the magnetic induction of a spin wave and the change of its electric field are interdependent: in the ferrite layer, there is a plane on which the electric field amplitude is zero and which is simultaneously a boundary between the curls of the magnetic induction. It is found out that the directions of the magnetic field and wave magnetic induction vectors are substantially different in the ferrite plate, although these vectors coincide in the half-spaces surrounding the plate.     

Electromagnetic resonances and Q factors of a chiral sphere

A study of electromagnetic resonances of an isotropic chiral sphere is presented. The characteristic equation of a chiral sphere, which is complex and transcendental, is obtained by forming solutions of the electromagnetic field for a chiral sphere in terms of the spherical vector wave functions. The characteristic equation is solved by using a computer. Resonant frequencies and Q factors of the first few modes for relative permittivities of two and ten are reported and discussed. These modes are hybrid modes. They are classed as either hybrid electric (HE) modes or hybrid magnetic (HM) modes. Chirality is observed to have a significant effect on the resonances of a sphere.     

The influence of a metal screen and magnetic wall on the vector line pattern of the high-frequency field of a surface spin wave

Equations for vector lines of the magnetic field and magnetic induction of a spin wave propagating perpendicularly to an external magnetic field in a dielectric–ferrite–dielectric structure tangentially magnetized to saturation and bounded on both its walls by a perfect conductor or a perfect magnetic wall are obtained. The vector line patterns of these magnetic quantities are calculated for the case when one of the dielectrics is a vacuum half-space. It is shown that the spin wave in a ferrite plate and in such structures may be considered as vortices of magnetic induction propagating in time and space. A relationship between the position of vortices of magnetic induction and the variation in the electric field of the spin wave is found. It is established that, in the structures under consideration, the vector lines do not form vortices.     

Development of the Microstrip Circulator with a Magnetized Ferrite Sphere in Millimeter Wave Band

In this paper, a novel microstrip circulator with a magnetized ferrite sphere is proposed for various millimeter wave communications. A three-dimensional Finite-Difference Time-Domain (FDTD) approach for the analysis of this ferrite sphere based microstrip circulator is first presented. The electromagnetic fields inside the ferrite junction are calculated using special updating equations derived from the equation of motion of the magnetization vector and Maxwell's curl equations in consistency. Frequency dependent insertion loss, isolation and reflection loss of circulator are calculated over a wide band of frequencies with a single FDTD run. Experimental results at Ka band are presented and compared with theoretical simulations. As a result, a good agreement is found between them.     

论电磁惯性

伟大的物理学家牛顿首先提出了力学惯性定律:"每个物体将继续保持其静止或沿一直线做匀速运动状态,除非有力加于其上迫使它改变它改变这种状态."而本文则在电磁领域提出相应的电磁惯性-每个电磁波都倾向于保持球三维或圆二维状态向外传播,除非有外加源或边界迫使它改变这种状态.文中,还把这一思想进一步扩展为电位ψ和电荷σ的静电惯性.     

A new Ka-band microstrip Y-junction circulator with a ferrite sphere

A novel microstrip circulator with a magnetized ferrite sphere is proposed for millimetre wave communications. A three-dimensional finite difference time-domain (FDTD) approach for the analysis of this ferrite sphere-based microstrip circulator is presented. The electromagnetic fields inside the ferrite junction are calculated by using special updating equations derived from the equation of motion of the magnetization vector and Maxwell's curl equations in consistency. Frequency-dependent insertion loss, isolation and reflection loss of circulator are calculated over a wide band of frequencies with a single FDTD run. Experimental results at the Ka-band are presented and compared with theoretical simulation. Good agreement is found between them.     

Plane electromagnetic wave scattering by transversely magnetized ferrite cylinder

The paper is devoted to the problem of scattering of plane electromagnetic wave by transversely magnetized ferrite cylinder. Exact analytical expressions for all partial cylindrical modes are obtained by solving Maxwell’s equations for transversely magnetized ferrite medium in cylindrical coordinate system. They are represented as the power series expansion and then are used to formulate and to solve the boundary problem. Numerical calculations of scattering patterns are also presented. Particular attention is paid to the possibility to control the scattering pattern by the external magnetic field.     

3-D modeling and analysis of meander-line-coil surface wave EMATs

Surface wave electromagnetic acoustic transducers (EMATs) are becoming preferred sensors of automatic inspection systems for the detection of surface-layer defects in hostile environments. Aiming at establishing a 3-D model for meander-line-coil surface wave EMATs operating on the Lorentz principle, a novel modeling method is proposed by combining numerical calculations and analytical solutions with special attention to the influence of the dynamic magnetic field. Simulation and analysis find that the frequency of the surface waves due to the dynamic magnetic field is twice that due to the static magnetic field; the excitation of surface waves with two frequencies can effectively improve the sensitivity of EMATs to flaws; and the force due to the dynamic magnetic field generates surface waves more efficiently than that due to the static one when the excitation current exceeds 528.9 A. The accuracy of the established model is verified by experiment.     

两层各向异性介质球电磁散射球矢量波函数解

在无源各向异性铁氧体和等离子体介质的球矢量波函数基础上,利用第一、二类球Bessel 满足相同的微分方程和递推关系,给出了各向异性铁氧体球涂覆均匀等离子介质对平面波散射的理论公式,并给出数值计算的结果,预计本文结果可应用于微波器件以及目标特性等领域。