Ferrite Medium Research Articles

Complex Eigenmodes and Eigenfrequencies in Electromagnetics

A comprehensive treatment on complex eigenmodes is presented for general lossy traveling-wave electromagnetic structures. The per unit length propagation phase shift ( β)-dependent complex eigenfrequencies Ω(β) are mapped to frequency-dependent complex propagation constant γ(ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) for a variety of electromagnetic structures. Rigorous procedures are presented to compute the complex eigenmodes of both uniform and periodic electromagnetic structures, confirmed using full-wave simulations and known analytical results. We further present two mapping procedures for arbitrary uniform and periodic structures, where the known {Ω-β} relationship is expressed using rational polynomial expansions. Consequently, replacing {Ω, jβ} with {ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , γ} in the known {Ω-β} relation, a characteristic equation is formed, which is then numerically solved for the propagation constant γ, representing the physical dispersion relation ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (β) and the frequency-dependent attenuation relation α(ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) of the structure. The mapping procedure is demonstrated for a variety of cases, including an unbounded uniform media, a rectangular waveguide, a Drude dispersive metamaterial, a biased ferrite medium, a periodic dielectric stack, and a periodic rectangular waveguide. The exact propagation characteristics have been successfully retrieved in all cases across both passbands and stopbands across frequency.

Transverse electric surface waves in ferrite medium surrounded by plasma layers

The theoretical analysis of transverse electric surface waves in ferrite medium surrounded by isotropic plasma layers is presented in this manuscript. Maxwell’s equations in differential form are used, and we impose the boundary conditions to acquire the dispersion relation to formulate the proposed structure. The influence of number density, separation distance between the layers of plasma, and dielectric permittivity of ferrite film on the normalized propagation constant is studied. It is concluded from the result obtained that if the number density and values of dielectric permittivity of ferrite film increases the propagation constant Re(β) tends to decreases whereas the increase in separation distance between the layers of plasma tends to increase the propagation constant Re(β). Furthermore, to verify the surface waves, the normalized field distribution for plasma medium as well as ferrite medium are also presented in this manuscript. The present work has potential applications in communication, drug delivery, cancer treatment, and ferrite sensing waveguide structures in the GHz frequency regime.

Efficient analysis of metal and dielectric rods in rectangular waveguide with ferrite magnetized transversely

ABSTRACTThis paper presents a new analytical method based on mode matching technique for a waveguide full of anisotropic material with rods. It is proved that mode matching technique is applicable for the waveguide with anisotropic materials. The problem is considered as a 2D electromagnetic problem assuming no field variation normal to the waveguide length. Incident and scattered fields from circular cylinder rods in ferrite medium are expanded with cylindrical modes, and the fields in the waveguide ports are expanded using progressive and regressive modal summations. In both regions, extraordinary wave number is considered for the fields. Finally, the hybrid mode matching between guided and cylindrical modes is done by projecting continuity equations in the circular boundary containing the rod. The fast Fourier transform is used to solve the matching in the presented method. It is shown, that the new method runs faster than commercial software packages, with very good accuracy.

Free Arrangement Wireless Power Transfer System With a Ferrite Transmission Medium and Geometry-Based Performance Improvement

A free arrangement wireless power transfer system with a ferrite transmission medium and geometry-based performance improvement method are introduced here. The proposed system addresses the efficiency collapse caused by misalignment or increased distance between the transmitter and receiver coils, that is, receivers can be located anywhere on the plate-shaped system, which can be applied to a table, wall, or floor to supply electrical power as needed. Despite its high cost, ferrite is advantageous over air as a medium as the latter diminishes the efficiency at a distance or misalignment. Further, ferrite reduces the transmitter volume and number of coil turns, which is useful for practical applications. Skewed-shape coil windings with higher effective mutual inductance than unskewed structures are used in this system to increase power transfer efficiency. The improvements from the ferrite and coil-winding geometry are verified through Ansoft Maxwell v14.0 and MATLAB simulations. Four prototypes of the proposed system are fabricated and validated at 100 kHz. The highest transfer efficiency at the farthest distance, 55 cm, is 17.5% with the 4-cm-skewed ferrite structure, whereas no power is delivered beyond 10 cm in air. Consequently, the proposed system achieves wider power transfer area and better efficiency without additional power and coil windings while the system complies with the guidelines provided by International Commission on Non-ionizing Radiation Protection (ICNIRP) and IEEE for human safety. This article is accompanied by a demonstrating video.

Multistage converter of high-voltage subnanosecond pulses based on nonlinear transmission lines

This paper presents new experimental data that enable the observed processes in nonlinear ferrite lines to be related with the theoretical positions of the spin waves of the magnetization precession under the conditions of a high-power microwave. Such an approach has not been considered in earlier discussions on the subject and can contribute to the theory of the generation of oscillations in a gyromagnetic ferrite medium. These new aspects were used to design a new type of generator. The specific feature is the presence of regularity in the ferrite lines in the generation mode of microwave oscillations. The repeating regularity enabled the implementation of multistage pulse shape converters capable of operating in two modes and providing extreme parameters of the output pulses. Two variants of multistage converters of nanosecond high-voltage pulse shapes with a duration of ∼4 ns at a half-height and with an amplitude of −500 kV were designed and tested. The assembly of the converters and the driving generator are described in the stationary setup. In the first case, the rise time shortened to ∼45 ps, and the amplitude increased to −850 kV due to the sharpening of a pulse and the formation of a shock wave by the cascade of three nonlinear transmission lines. A record rate for the increase of the leading peak voltage of ∼15.5 MV/ns was reached. In the second case, the new approach for the generation of a sequence of subnanosecond pulses was presented and tested, and each pulse of the previous stage was modulated by the next stage doubling the number of pulses while conserving a deeper modulation. As a result, at the top of the incident pulse, a sequence of subnanosecond peaks with a large modulation depth (∼70%) was formed when the maximum voltage amplitude reached −700 kV. The results of the emission of such pulses are also presented.

Deformation Behavior of a Double Soaked Medium Manganese Steel with Varied Martensite Strength

The effects of athermal martensite on yielding behavior and strain partitioning during deformation is explored using in situ neutron diffraction for a 0.14C–7.14Mn medium manganese steel. Utilizing a novel heat treatment, termed double soaking, samples with similar microstructural composition and varied athermal martensite strength and microstructural characteristics, which composed the bulk of the matrix phase, were characterized. It was found that the addition of either as-quenched or tempered athermal martensite led to an improvement in mechanical properties as compared to a ferrite plus austenite medium manganese steel, although the yielding and work hardening behavior were highly dependent upon the martensite characteristics. Specifically, athermal martensite was found to promote continuous yielding and improve the work hardening rate during deformation. The results of this study are particularly relevant when considering the effect of post-processing thermal heat treatments, such as tempering or elevated temperature service environments, on the mechanical properties of medium manganese steels containing athermal martensite.

Analysis of a fast-acting waveguide ferrite phase shifter with longitudinal magnetization phasing structure

The electrodynamic analysis and calculation of the phasing structure of a waveguide ferrite Faraday phase shifter with longitudinal magnetization of a ferrite rod with a square cross-section are performed. In the strict electrodynamic formulation, the Galerkin method solves the key problem for the design of the phase shifter: the problem of eigenwaves finding with a second-order differential magnetic operator in the projection procedure for a rectangular waveguide with a transversely inhomogeneous ferrite-dielectric filling under longitudinal magnetization. The problem is reduced to solving the complete eigenvalue problem of a complex matrix. The computational algorithm, implemented as a computer program in DELPHI, gives in one procedure the numerical values of the coefficients of the decomposition of fields in the form of eigenvectors of the matrix, and the coefficients of wave propagation in the form of its eigenvalues. The results of calculations of the phasing structure activity for two particular cases of its implementation are presented: on the basis of a ferrite rod both with a conductive coating and without a coating, it is shown that in the second case the activity of the phase shifter is 1.5 times higher. For the real parameters of the ferrite medium, the length of the phasing structure is calculated depending on the transverse dimensions of the ferrite rod and the square waveguide, which ensures the creation of a 360° controlled phase shift.

Unusual penetration effect in ferromagnetics. Negative refraction under tangential wave incidence.

In this paper we study behaviour of a refracted wave within a ferrite medium and a reflected wave in vacuum if an incident wave propagates along the interface in an isotropic medium. It is shown analytically that a plane harmonic wave can transmit from an isotropic medium to anisotropic medium in this exotic case. It is shown also that wave behaviour in this case is analogous to wave bahavior in a metamaterial. The wavenumbers of the refracted waves and the Poyting vectors are found. The reflection and transmission coefficients are investigated also.

Efficient Three-Step LOD-FDTD Method in Lossy Saturated Ferrites With Arbitrary Magnetization

A three-step unconditionally stable locally one-dimensional finite-difference time-domain method is proposed to represent an arbitrarily magnetized lossy ferrite medium. The small loss in the saturated ferrite is introduced to the algorithm through a simple explicit relation. A step-by-step procedure is established to minimize the number of operations and variables. It is shown that the processing time and occupied memory variables in the proposed method are about 90% and 50% of those of the one-step leapfrog alternating direction implicit method, respectively. The accuracy and stability of the method are verified through the simulation of wave propagation in two ferrite-loaded devices, including a microstrip phase shifter, and a stripline circulator.

EQUIVALENT VERIFICATION OF THE EFFECT OF THE IONOSPHERIC FARADAY ROTATION ON GEO SAR IMAGING BY FERRITE

In geosynchronous earth orbit synthetic aperture radar (GEO SAR) working system, the radar signal travelling through the atmosphere is sensitive to the ionosphere. One of the effects is the Faraday rotation under geomagnetic field, which is similar to the phenomenon when the signal traveling through a ferrite medium. So based on the theoretical inference, we semi-physically simulate Faraday rotation of the ionosphere with that of the ferrite in the ground, which is one of the experiments of the ground railway prototype testing for GEO SAR system. The measurements of a mountain without ionospheric Faraday rotation and under the equivalent Faraday rotation of ionosphere are given experimentally. Imaging studies show that the influence of the ionosphere Faraday rotation on the distributed targets imaging is not visually obvious. Our work provides experimental basis for the GEO SAR to successfully image on the satellite.

Finite-difference time domain method for the analysis of radar scattering characteristic of metal target coated with anisotropic ferrite

A metal cylinder coated with anisotropic ferrite material is analyzed using the finite-difference time-domain method (FDTD) in this paper, and the bistatic radar cross-section (RCS) is obtained. The new method of electromagnetic scattering by magnetized ferrite medium is analyzed in detail based on the FDTD. To exemplify the availability of the algorithm, bistatic RCS of a magnetized ferrite cylinder is computed, and the numerical results are the same as the shift operator FDTD (SO-FDTD), which shows that the proposed FDTD method is correct and efficient.

Efficient MT-Based Compact FDTD Algorithm for Longitudinally-Magnetized Ferrite-Loaded Waveguides

In this work, a compact finite-difference time-domain (FDTD) algorithm with a memory-reduced technique is proposed for the dispersion analysis of rectangular waveguides either fully or partially loaded with longitudinally-magnetized ferrite. In this algorithm, the divergence theorem is used to eliminate the longitudinal components of the electric and magnetic flux densities. The mobius transform (MT) technique is applied for the first time to obtain the equations relating the magnetic field to the magnetic flux density in a ferrite medium. Some examples are presented to validate the obtained algorithm with numerical results: good agreement is obtained with a significant reduction in the memory space requirement compared to the conventional algorithm.

A Stepped-Pole Writer to Minimize Side Erasure on Barium Ferrite Tape

Side erasure is investigated for non-oriented and perpendicularly oriented barium ferrite particulate tape media without a soft-underlayer. While notching is efficient to avoid side writing from the leading pole, the perpendicular head fields originating from the outer edge of the trailing pole result in curved transitions and non-negligible side erasure. We find that such side erasure effects can be suppressed by recessing part of the trailing pole, thereby forming a stepped pole. Magnetic force microscopy and cross-track profiling experiments demonstrate the efficacy of this novel stepped-pole writer design to minimize side writing effects in non-oriented and perpendicular particulate tape media. This writer geometry will enable tape recording at 50 ktpi and beyond.

Planar Thin-Film Servo Write Head for Magnetic Tape Recording

We present a planar thin-film servo write head for writing timing-based servo patterns. The planar head operates at low current ( ~ 100 mA) with nanosecond switching times. The planar head can handle dc current, enabling trailing-edge writing. Magnetic force microscopy measurements of the transitions written by the planar head and a conventional commercial servo write head on longitudinal metal particle and nonoriented barium ferrite media were made to assess the quality of the written transitions. The transition response width PW50 is found to be independent of the tape velocity during write for the planar head. For the conventional head, PW50 is larger and increases with the tape write velocity. The reduced PW50 results in larger readback signal amplitude and hence an improved track-follow performance. The faster switching capability of the planar head enables formatting at higher tape velocity.

New Scattering Matrix Model for Modeling Ferrite Media Using the TLM Method

This paper aims to extend the transmission line matrix method with a hybrid symmetrical condensed node (HSCN) to model ferrite media in the time domain. To take into account the anisotropy and dispersive properties of ferrite media, equivalent current sources are incorporated into supplementary stubs of the original HSCN. The scattering matrix of the proposed HSCN is provided, and the validity of this approach is demonstrated for both transversely and longitudinally magnetized ferrites. Agreement is achieved between the results of this approach and those of the theoretical and the finite-difference time-domain method.

A Second-Order Accurate Time-Stepping Algorithm for Dominant Mode Propagation in Ferrite Media

This communication presents a fully second-order accurate time-domain simulation scheme that incorporates magnetic materials operating in the dominant mode. The proposed scheme is a modification of the Yee scheme by incorporating the Landau-Lifschitz equation of motion including the dominant and loss terms. Additionally, a rigorous dispersion analysis is presented for the proposed scheme. It is demonstrated that the proposed scheme has no numerical losses (when the phenomenological loss term is set to zero), and the pertinent resonant frequencies experience a second-order shift as a consequence of the numerical discretization.

Effective longitudinal magnetic response of magnetic metamaterial in the GHz frequencies

PurposeThe purpose of this paper is to study the microwave behaviour of effective magnetic permeability for two‐component ferrite like metamaterial medium in the direction of a biasing magnetic field. The metamaterial medium is presented as an infinite host dielectric material (air) with periodically embedded ferric cylindrical and spherical inclusions saturated with an external dc magnetic field. The study is based on the effective medium theory developed for polycrystalline metaferrites. The simulations show that the presented metamaterial can exhibit the ultra‐low refractive index (ULI) phenomenon and the phenomenon of negative magnetic permeability for the case of microwave propagation in the direction of bias.Design/methodology/approachThe obtained results are based on the wave long approximation of permeability tensor of the presented metamaterial media obtained earlier by the first author. Using the standard approach, the authors apply the above expressions for the microwave propagation in direction of biasing dc magnetic field considering different polarization of the incident microwave.FindingsThe considered artificial material media can become either material with a ULI or with negative values in the GHz frequencies.Originality/valueThe paper is concerned with part of the theory of a new generation of artificial ferrites.

Composite Electromagnetic Wave Absorber Made of Ni-Zn Ferrite Particles Dispersed and Isolated in an SiO&lt;sub&gt;2&lt;/sub&gt; Medium

In order to design a ferrite absorber that can be used at frequencies of several GHz, the frequency dependences of the relative complex permeability μr*, the relative complex permittivity εr*, and return loss were investigated for a composite made of Ni-Zn ferrite and SiO2. When ferrite particles were dispersed and isolated in an SiO2 medium, the frequency dependence of μr* was different from that for a composite made of SiO2 particles dispersed and isolated in the ferrite medium. Moreover, when ferrite particles were isolated and a suitable mixture ratio of ferrite and SiO2 was selected, the return loss was less than −20 dB at frequencies of several GHz. The dispersion states of ferrite and SiO2 particles are thus important factors to design an absorber, and improvement in the absorption characteristics of the ferrite tile which is used as a practical absorber could be achieved using a composite made of Ni-Zn ferrite particles dispersed and isolated in an SiO2 medium.

Compact Tunable Left Handed Ferrite Transformer

In this paper, a novel compact and tunable impedance transmission line transformer is presented for the first time. The transformer is designed using a left handed coplanar waveguide transmission line on a ferrite substrate. Based on the dispersive properties of the ferrite medium, the theoretical study of the transformer has been carried out using its equivalent circuit analysis and the composite right / left handed transmission line theory. The theoretical study was verified through full wave electromagnetic numerical simulations. The results show that the transformer matches a 25 Ω load to a 50 Ω line with tunability from 2.55 GHz to 3.2 GHz. The return loss at center frequency is better than 20 dB with insertion loss better than -1 dB. The transformer has a very compact size with dimensions of 4.25 × 21 mm2, showing approximately 64% reduction in size in comparison with a conventional right-handed transformer within the same operating frequency band. Moreover, the proposed coplanar waveguide transformer configuration has smaller demagnetization factor and hence it requires smaller DC magnetic bias values compared to microstrip configuration.

A Generalized Time-Stepping Algorithm for Electromagnetic Wave Propagation in Ferrite Media

A time integration scheme is described for simulations of electromagnetic waves within a fully saturated ferrite medium. By considering Maxwell's equations in conjunction with the torque equation of motion for electron precession, we show that a stable second-order scheme can be achieved using both central differences and averages. The scheme is validated using a stripline phase shifter as a test case. Not only does the simulation agree quite well with results produced by a popular frequency-domain, finite element solver, the data also exhibits a very desirable, low-loss, phase shift effect.