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.     

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.     

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.     

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。     

Ie transmission properties of stratified chiroferrite media with obliquely incident plane wave

A parameter study of electromagnetic wave propagating through the air-chiro ferrite inter face and through a chiro ferrite slab is presented, and such bianisotropic medium can be made from chiral and gyrotropic ferrite materials artifically. The partial differential equations of the fourth order defining the field components E_y and H_y in chiroferrite are derived. The influence of different constitutive parameters on the transmission coefficients and refraction angles of transmitted fields are demonstrated. The results show that chirality causes strong effect of energy conversion between mode 1 and 2.     

Time-domain electromagnetic plane waves in static and dynamicconducting media. II

For pt.I see ibid., vol.36, no.3, p.221 (1994). The electromagnetic field inside a lossy half-space for the case of a transient electromagnetic plane wave impinging on the half-space from free space is derived. The losses in the half-space are modeled by assuming either a static (J=σE) or a dynamic (τ∂J/∂t+J=σ₀E) conducting medium. Solutions are derived directly from the first order system of partial differential equations, i.e. the Maxwell equations. Plots for the total fields at the half-space boundary are given and expressions for the fields anywhere inside the half-space based on these boundary fields are given. Asymptotic formulae for late and early times are derived for the case of a step function as well as a square pulse plane wave     

Photon/magnon conversion near a material interface

Direct coupling between electromagnetic waves and spin waves caused by an abrupt discontinuity in material parameters is studied. It is shown that the simultaneous presence of an evanescent and propagating wave can lead to the conversion of electromagnetic power to exchange power. The partial conversion of an electromagnetic wave travelling in air, and incident normally upon a ferromagnet, is analysed in detail for the case when the material is uniformly magnetised to saturation along the direction of propagation.     

The Point-Matching Solution for Magnetically Tunable Cylindrical Cavities and Ferrite Planar Resonators

This paper presents an exact field theory treatment for a cylindrical cavity containing a full-height triangular ferrite post as well as for ferrite planar resonators of arbitrary shape. The knowledge of the resonant frequencies of the cavity is essential for the construction of circulators with a triangular ferrite post; those of the planar circuits are needed for the design of microwave integrated circuits. The treatment is general and depends neither on the location of the ferrite post inside the cavity nor on the geometry of the planar resonator. The solution of the wave equations in the ferrite material and in a possible surrounding air region is written as an infinite summation of cylindrical modes. In the case of the cavity, the individual modes are exactly matched along the internal cylindrical metallic boundary of the cavity. The fields at the ferrite-air interface in both cases are matched using the point-matching technique, which leads to a finite system of homogeneous, simultaneous equations for which the determinantal equation must be zero. An example of a cavity with a triangular ferrite post is studied and calculated, and measured results are compared. Furthermore, examples of application of the theory on triangular and quadratic planar resonators are described and compared with published experimental measurements.     

Efficient broadband excitation of the n = 0 surface magnetostatic waves in a y.i.g. slab

This letter describes an efficient method for exciting the lowest-order surface magnetostatic wave in a transversely magnetised single-crystal y.i.g. slab. The total coupling loss from an electromagnetic wave to a surface magnetostatic wave and back into an electromagnetic wave is measured to be less than 2.5dB, from 3.2 to 3.8GHz. The propagation characteristic of the surface magnetosatic wave is also discussed.     

Propagation characteristics of a circular waveguide filled with a chiroferrite medium

A chiroferrite is made from chiral objects immersed in a magnetically biased ferrite. A waveguide including a chiroferrite is anticipated to possess some novel features due to the presence of chirality in combination with anisotropy. In this paper, the propagation characteristics of a circular metal waveguide filled with a chiroferrite medium are investigated by an analytical procedure. The equations of relations between the transverse components and the longitudinal ones of electromagnetic fields in general chiroferrite waveguides are derived in a cylindrical coordinate system. The coupled wave equations for the longitudinal electric and magnetic fields are decoupled into two Helmholtz equations which are then solved analytically. The characteristic equation is formulated for the circular chiroferrite waveguide. Propagation constants varying with the structural and material parameters have been calculated for several lower chiral modes. A number of interesting features have been revealed by the numerical results.     

Electromagnetic fields with arbitrary wave impedances generatedinside a TEM cell

It is shown that arbitrary electromagnetic fields and wave impedances can be generated inside a transverse electromagnetic (TEM) cell for RF susceptibility testing. This is achieved by simply exciting one port and terminating the other port with appropriate loads. Thus, TEM cells are not limited to producing a planar field environment with the free-space impedance of 377 Ω, but can also be used to generate high-impedance or low-impedance fields for special testing needs. Experimental results for only three load impedances are described. In principle, many other loads including reactive terminations could be used to create a particularly desired field and wave impedance inside the TEM cell     

A survey of the near-field far-field inverse scattering inverse source integral equation

The Kirchhoff direct integration of the scalar wave equation is reviewed, and some properties of the Kirchhoff surface integral are discussed, from the perspective of the inverse scattering inverse source problem. A modified Kirchhoff surface integral is introduced, leading to a Fredholm integral equation of the first kind for the unknown sources (induced by the incident field) inside a volume in terms of the (scattered) fields on the surface enclosing this volume. The properties and physical meaning of this integral equation are discussed. A generalization of this integral equation for the vector electromagnetic wave equations is presented.     

Propagation of transients in dispersive dielectric media

The propagation of transient electromagnetic fields in dispersive dielectric media is studied. The dielectric medium is assumed to be linear, isotropic, and homogeneous, and is described by the Debye model. Incident fields are assumed to be transverse electromagnetic plane wave pulses. The dielectric body can assume the form of infinite half space or an infinite circular cylinder, either of which may be homogeneous or stratified. The electric fields induced in the dielectric are calculated from time-domain Maxwell's equations using the finite-difference time-domain method.<>     

Analysis of the power coupling from a waveguide hyperthermiaapplicator into a three-layered tissue model

The power deposition from a rectangular-aperture flanged waveguide into a three-layered stratified tissue medium is analyzed theoretically. The fields inside the tissue layers are expressed in terms of Fourier integrals satisfying the corresponding wave equations, while the fields inside the waveguide are expanded in terms of the guided and evanescent normal modes. An integral equation is derived on the aperture plane of the flanged waveguide by applying the continuity of the tangential electric and magnetic fields. This integral equation is solved by expressing the unknown electric field in terms of the waveguide mode fields and by applying a Galerkin procedure. The electromagnetic fields inside the tissue medium are then determined and patterns of the deposited power at frequencies of 432 MHz and 144 MHz for apertures of 5.6×2.8 cm² and 16.5×8.3 cm², respectively, are computed and presented     

Field Theory Treatment of H--Plane Waveguide Junction with Triangular Ferrite Post

This paper presents an exact field theory treatment for the H-plane waveguide junction with three-sided ferrite prism. The treatment is general, being independent of the geometrical symmetry of the junction, the number of ports, and the location of the ferrite post inside the junction. The solution of the wave equations in the ferrite post and in the surrounding region is written in the form of an infinite summation of cylindrical modes. The fields at the ferrite-air interface are matched using the point-matching technique. This results in two amplitudes for the cylindrical modes describing the fields in the air region in the form of a matrix. The fields at the arbitrary boundary between the air region and the waveguides are also matched using the point-matching technique. This results in a finite system of nonhomogeneous equations in the field amplitudes. The three-port waveguide junction circulator with central triangular ferrite post is analyzed using this technique. Two specific arrangements are considered. In the first arrangement, the points of the triangles are in the centers of the waveguides, and in the second, the sides of the triangles are in the centers of the waveguides. The method used in this paper can also be applied to study the effect of the ferrite-post geometry on the circulator performance in order to seek the best possible circulator structure. Excellent agreement has been found between published experimental measurements and the numerical results obtained by this technique in the case of a waveguide junction circulator with cylindrical ferrite post.     

Scattering by an inhomogeneous dielectric/ferrite cylinder ofarbitrary cross-section shape-oblique incidence case

A moment method (MM) solution is developed for the fields scattered by an inhomogeneous dielectric/ferrite cylinder of arbitrary cross-section. The incident field is assumed to be a plane wave of arbitrary polarization with oblique incidence with respect to the axis of the cylinder. The total electric and magnetic fields are the unknown quantities in two coupled equations from which a system of linear equations is obtained. Once the total electric and magnetic fields within the cylinder are computed, the scattered fields at any other point in space can be calculated. It is noted that for the case of oblique incidence, the scattered field has TE_z and TM_z polarized fields regardless of the polarization of the incident field. The echo widths of cylinders and shells of circular, semicircular, and rectangular cross section are calculated for TE_z and TM_z polarized incident fields. It is shown that the results obtained for dielectric/ferrite cylinders and shells of circular cross section with the solutions developed here agree very well with the corresponding exact eigenfunction solutions     

Radiation from harmonic sources in a uniformly moving medium

In this paper the Maxwell-Minkowski equations are used to find a general integral for the electromagnetic fields in an infinite moving medium. The medium is assumed to be homogeneous, isotropic, and to move with a constant velocity much less than the speed of light. Only time-harmonic fields are considered. A wave equation for the electric field is derived and is integrated by means of a Green's Identity and an appropriately defined Dyadic Green's Function. The result gives the electric field inside a volume of space in terms of known sources in the volume and the tangential components of the electric and magnetic fields over the enclosing surface. Finally, the fields radiated by a point dipole are found.     

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.     

Analysis of energy coupling into spheroidal ferritic implants forhyperthermia applications

The coupling of energy of RF power into lossy tissues using a needle-shaped ferromagnetic implant excited by an externally applied current loop is analyzed theoretically. The ferritic implant is assumed to be of prolate spheroidal shape, while the tissue medium is modeled as a lossy sphere. The electromagnetic fields inside the ferritic implant, the surrounding lossy tissue, and the free space are appropriately expressed in terms of spherical and spheroidal wave functions. Application of the boundary conditions results in an infinite system of equations for the unknown field expansion coefficients. This system is truncated and solved and the electromagnetic field is computed numerically. Absorbed power density inside the implant and the surrounding medium is computed, and the efficiency of the method in producing in-depth energy deposition is examined