Application of Ferrite to Electromagnetic Wave Absorber and its Characteristics

An electromagnetic wave absorber utilizing ferrite or rubber ferrite composed of ferrite powder and rubber is described. In our investigation, the existence of a matching frequency f/sub m/ and a matching thickness t/sub m/ has been found. The terms f/sub m/ and t/sub m/ mean that the ferrite which is backed with a conducting plate can be a perfect absorber only under the conditions that the frequency of the incident wave is f/sub m/ and that the thickness of the ferrite is t/sub m/.Each ferrite has two matching frequencies f/sub m1/, f/sub m2/, (f/sub m1相似文献   

Electromagnetic wave absorbing characteristics of Ni-Zn ferritegrid absorber

The reflection loss of Ni-Zn ferrite grid absorber is studied in the low frequency limit which the period of the array is small compared with wavelength. The relative equivalent complex permeability and permittivity with air volume fraction is obtained using the Hashin-Shtrikman (1962) upper-bound formula. The impedance matching conditions for maximum electromagnetic wave absorption are obtained by the “contour map method.” Two impedance matching thicknesses and frequencies are compared with theoretical matching relationships derived under the limiting case of impedance matching formula. As the air volume fraction increases, the first matching frequency, f_m1 remains nearly constant, while the second one, f_m2 decreases and approaches f_m1. Therefore, the absorption band of a ferrite grid absorber is broader than that of the single layered ferrite plate absorber     

Theoretical Analysis of the Operation of the Field-Displacement Ferrite Isolator

A theoretical analysis of the resistance-sheet isolator is carried out, and numerical solutions are obtained for the forward and reverse propagation constants of the distorted dominant mode in a rectangular waveguide containing a transversely magnetized thick ferrite slab displaced slightly from the side wall. The microwave electric field patterns within the waveguide are plotted for several values of the physical design parameters of the isolator for which experimental performance data have been reported. Field patterns are used to describe the principles of the isolator and to select the optimum values of slab thickness, internal dc magnetic field, ferrite magnetization, and location of the slab in the waveguide for the idealized isolator. Evidence is presented to show that it is necessary to use a comparatively thick ferrite slab located in a very small usable range of distances from the side wall. The appropriate value of internal dc magnetic field is simply related to the magnetization of the ferrite and to the frequency. It has not been necessary to take into account the perturbing effects of the resistance card or matching techniques in order to explain the basic design principles.     

Surface wave along a ferrite rod magnetized below saturation

Surface waves supported by a ferrite rod, magnetized longitudinally near and below saturation, are studied experimentally using the surface wave resonator technique. Two types of slow waves are found to exist. Their propagation constants depend on the dc magnetic field and rod size. They are interpreted as theHE_{11}mode positive and negative circularly polarized surface waves. For pure circularly polarized waves, a magnetized ferrite is considered as a dielectric with nontensor permeability. A calculation of the propagation constant of these circularly polarized surface waves, based on the dielectric analogy, is made. The agreement between calculation and measurement is close.     

Millimetre-wave second-harmonic Gunn-diode oscillator with magnetic tuning

A second-harmonic Gunn-diode oscillator with a rectangular waveguide resonator for the fundamental frequency has been designed and tested in the SO GHz frequency range. A longitudinally magnetized ferrite slab, placed in the resonator, makes possible a frequency decrease of 0 to 250 MHz when a static magnetic field of 0 to 220 Oe is applied.     

有关电磁噪声复合吸收体技术的介绍（二）

电磁噪声吸收的机理 复合吸收体中电磁噪声被吸收的现象可以在近场和远场应用中被分别解释。在近场应用中,吸收体的磁损耗在吸收高频噪声的过程中发挥着重要的作用。复合吸收体是磁性材料,其特征磁导率在1O到200之间。在低频情况下,这些吸收体具有稳定的磁导率特征。但在更高的频率上,它们显示出二阶磁导率效应。而且,在场强度很高的情况下,     

The nonreciprocity of microwave transmission along a bianisotropic-ferrite metastructure

Propagation of microwaves along a plane layered structure containing a bianisotropic and a magnetized ferrite layer is theoretically investigated. The dispersion equation that allows taking into account an air gap or an active layer (SPASER) located between these layers is derived. This equation is numerically solved with allowance for the dispersion characteristics of the ferrite and bianisotropic metamaterial, and, with the help of the obtained solution, the spectra of the slowing factor and nonreciprocity parameter of the wave transmission in the structure are found. The influence of the magnitude and direction of the external magnetic field and of the gap thickness on the nonreciprocity parameter is considered. The validity of the conclusion (drawn from experiments) that it is possible to provide for the nonreciprocal transmission of signals at frequencies substantially exceeding the ferromagnetic resonance frequency attainable in the presence of the available magnetic field is confirmed.     

Measurements of all complex permeability tensor components and theeffective line widths of microwave ferrites using dielectric ringresonators

A method of measuring all the complex permeability tensor components of microwave ferrites using a single cylindrical ferrite sample is described. Two dielectric ring resonators having the same height and internal diameter but different external diameters, operating on HE₁₁₁^± and H₀₁₁ modes respectively, are applied for these measurements. Permeability tensor components are computed from the measured resonant frequencies and Q factors of these resonators with and without the ferrite sample. Computations are based on the exact eigenvalue equations for these modes. Measurements of all permeability tensor components versus static magnetic field intensity, performed for different ferrite materials, generally confirm results obtained by earlier researchers, but they also contain certain aspects concerning relations between particular permeability tensor components below saturation     

Magnetic Nanocomposite for Potential Ultrahigh Frequency Microelectronic Application

Cobalt ferrite nanocomposites were investigated as example materials for microelectronic applications in the ultrahigh frequency range. Both static magnetic properties (magnetization versus applied field curve) and dynamic properties (complex permeability and permittivity at frequencies up to 1 GHz) were studied. When the ferritic density reached a certain level, the coercivity of the composite material decreased and the permeability increased noticeably. This phenomenon indicated the establishment of magnetic coupling between particles, which is necessary for magnetic nanocomposites to be used in electronic applications. Compared to magnetic composites made of micron-sized fillers, the magnetic loss of the nanocomposites was lower. However, the permeability of the nanocomposite was also lower. Cobalt zinc ferrite nanocomposites were prepared to explore the effect of composition, which revealed that the permeability of the magnetic nanocomposite could be improved by modifying the composition.     

Propagation properties of ferromagnetic insulator guide

In order to realize new ferrite planar devices for applications at millimeter-wavelength frequencies, the authors have developed nonreciprocal ferrite devices schemes for incorporating ferromagnetic layers in dielectric insulator guide geometries. Their research program involves both the calculation and the measurement of device characteristics. For the calculation, a method of effective permeability, in which the permeability is a tensor, is introduced to characterize the ferrite material. The propagation properties of the insular guide are calculated by using a single-mode approach. The calculated results for dispersion, dielectric, and conductivity losses show resonant behavior with the application of a magnetic bias field for a guide configuration in which the ferrite replaces the insular dielectric. Ferrite phase shifters, filters, isolators, and circulators are potential applications of this guide configuration. For the experimental part of the study, wave dispersion and attenuation were measured in a purely dielectric insular guide from 26.5 to 40GHz. In addition to these experiments wave attenuation was measured as a function of magnetic bias field for the case where a hexagonal ferrite platelet was mounted on the ground plane near the insulator guide. General agreement is found between calculated and measured attenuation     

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.     

Design of High-Performance Millimeter Wave and Sub-Millimeter Wave Quasi-Optical Isolators and Circulators

Faraday rotators using permanently magnetized ferrite materials are used to make quasi-optical isolators and circulators at millimeter wave and sub-millimeter wave frequencies that have far higher performance than their waveguide equivalents. This paper demonstrates state-of-the-art performance for four-port quasi-optical circulators with 60-dB isolation, 0.2-dB insertion loss, and better than 80-dB return loss for devices centered at 94 GHz. A method is presented for the accurate characterization of the complex permeability and permittivity of permanently magnetized ferrites via a series of frequency and polarization dependent transmission and reflection measurements. The dielectric and magnetic parameters for the sample are determined by fitting theoretical curves to the measured data. These fitted parameters are then used in a model for a complete quasi-optical Faraday rotator, including matching layers, allowing the accurate design and fabrication of these devices for any specific operational frequency band in the millimeter wave and sub-millimeter wave regime. Examples are given showing typical results and demonstrating how temperature cycling can significantly improve the temperature stability of these devices, while allowing fine tuning of the center frequency. We also indicate the performance possible at higher frequencies to above 1 THz and outline performance of truly planar isolators where lossy polarizer material is built into the Faraday rotator matching structure     

Characteristics of aperture coupled microstrip antennas on magnetized ferrite substrates

The method of moments in the spectral domain is applied to the full-wave analysis of aperture coupled microstrip antennas in the case where the substrate of the antennas is a layered medium containing magnetized ferrites. The subsectional basis functions used in the analysis make it possible to handle patch antennas and coupling apertures with right angle corners of arbitrary shape. The numerical results obtained show that antennas on ferrite substrates fed by single microstrip lines can radiate both circular and linear polarization, the polarization state being dependent on the orientation of the ferrites bias magnetic field. For a given polarization state, the matching frequency band of the antennas can be tuned over a wide frequency range by adjusting the magnitude of the bias magnetic field. Also, the polarization state can be continuously tuned from circular to linear within the same frequency band by adjusting both the magnitude and the orientation of the bias magnetic field. Some measurements are presented in order to check the validity of the numerical algorithm developed.     

Surface waves guided by a plate made from a bianisotropic resonance metamaterial

The dispersion characteristics, the distribution of energy fluxes, and the polarization of the magnetic field of surface waves formed in free space by a bianisotropic-material layer with resonance and anisotropic chirality, permittivity, and permeability are studied theoretically. The transmission and reflection spectra for lattices of resonance planar elements exhibiting magnetoelectric interaction are investigated experimentally. The nonreciprocity of microwave transmission in structures consisting of a lattice and a transversely magnetized ferrite plate is also investigated experimentally. The qualitative agreement of experimental results and theoretical predictions is established.     

结构型铁砂基复合电波吸收体研究

由天然尖晶石铁氧体（铁砂）为基制备的复合电波吸收材料，在７～１２ＧＨｚ，吸收率Ａ为１２～２７ｄＢ，匹配厚度ｄ为１．４ｍｍ。将几种铁砂基复合吸收材料制成双层结构电波吸收体，Ａ最大达４０ｄＢ，匹配厚度ｄ为１ｍｍ，频带增宽。这是一种廉价的吸收材料，其造价仅为一般铁氧体吸收材料的１／１０，有较大实用价值。     

Ferrite Polymer Composite for Improving the Electromagnetic Compatibility of Semiconductor Packaging

The complex permittivity and permeability of ferrite-filled polymer composites were studied at 50 MHz to 1 GHz, and their effects on the electromagnetic compatibility (EMC) of an integrated circuit (IC) package mounted on a printed wiring board (PWB) in the far- and near-field modes were investigated. Incorporating the ferrite particles into the polymer increased the real part of the complex permeability to 10–11 at 50 MHz, and the real part exhibited a frequency dependency over the applied frequency range (50 MHz to 1 GHz). The ferrite particle increased the magnetic loss (μ″ = 3–5) as well, which can absorb the magnetic energy of the incident electromagnetic wave. By coating the test IC package with the ferrite-polymer composite materials, the EMC level of the PWB was dramatically improved. This improvement may be due to the high magnetic loss of the ferrite-polymer composite.     

退火温度对铁基纳米晶带材高频磁导率的影响

采用单线圈法,利用Agilent E4991A射频阻抗/材料分析仪,研究了退火温度对铁基纳米晶带材的高频磁导率的影响。结果表明:经550℃退火处理的30μm厚样品磁导率实部,随频率增加而减小,在1MHz下为1210,在20MHz下为234,磁导率虚部有类似的变化趋势;比较了30μm厚样品经不同温度退火处理后磁导率的测量结果,得出550℃是一个比较理想的退火温度。     

Electromagnetic Wave Propagation in Lossy Ferrites

The square of the complex transverse propagation constant in a lossy, magnetized ferrite is found to be described approximately by a circle in the complex plane when the magnetic field is varied. A graphical method for obtaining approximate values for the transverse propagation constant when the wave number in the direction of the applied field is given and real is derived here. This method is used to find The power absorbed from an incident plane wave by A semi-infinite ferrite as a function of the magnetizing field amplitude.     

Theory and numerical calculations for radially inhomogeneouscircular ferrite circulators

This paper presents a new theory for the operation of microstrip and stripline circulators, specially set up to permit radial variation of all the magnetic parameters. A computer code, taking only a few seconds per calculated point on a modest computer, was developed from the theory, and calculated results are given. In the theory we develop a two-dimensional (2-D) recursive Green's function G suitable for determining the electric field E_x anywhere within a microstrip or stripline circulator. The recursive nature of G is a reflection of the inhomogeneous region being broken up into one inner disk containing a singularity and N annuli. G has the correct properties to allow matching to the external ports, thereby enabling s-parameters to be found for a three-port ferrite circulator. Because of the general nature of the problem construction, the ports may be located at arbitrary azimuthal angle φ and possess arbitrary line widths. Inhomogeneities may occur in the applied magnetic field H_app, magnetization 4πM_s, and demagnetization factor N_d . All magnetic inhomogeneity effects can be put into the frequency dependent tensor elements of the anisotropic permeability tensor. Numerical results are presented for the simpler but immensely practical case of symmetrically disposed ports of equal widths taking into account these radial inhomogeneities. Studies of breaking up the area into 1, 2, and 5 annuli are undertaken to treat specific inhomogeneous problems. The computer code which evaluates the recursive Green's function is very efficient and has no convergence problems     

Theoretical Analysis of Twin-Slab Phase Shifters in Rectangular Waveguide

The differential phase shift and the losses to be expected in phase shifters using two oppositely magnetized ferrite slabs located symmetrically in a rectangular waveguide have been calculated for various locations and thicknesses of the ferrite slabs. For small thicknesses of the ferrite slabs, the differential phase shift increases rapidly with increasing thickness reaching a maximum when the thickness is approximately 1/10 of the free space wavelength. The calculated insertion loss of a 360-degree phase shifter decreases with increasing slab thickness for small thickness, reaching a minimum when the thickness is approximately 1/25 of the free space wavelength. The minimum insertion loss calculated with the assumption that the imaginary part of the diagonal component of the permeability tensor is 0.01 and that dielectric loss can be neglected is approximately 0.85 dB. The peak power handling capability has also been analyzed. It can conveniently be summarized in terms of a high-power figure of merit. For reasonably high values of this figure of merit, a peak power capability of the order of 100 kW is anticipated.