Analysis and design of ferrite cores for eddy-current-killedoscillator inductive proximity sensors

Finite element modeling of ferrite cores used in the design of eddy-current-killed oscillator inductive proximity sensors was performed. Based on contemplation of the practical operation of the sensors, ferrite core geometries were compared with a reference core by the eddy-current power loss in a metal target at a fixed distance from the face of each transducer. Several of these cores were experimentally evaluated for sensing distance to verify the results of the simulation. It was observed that, for fixed coil, fixed target distance, and given target, the low-frequency sensing distance of a particular transducer is approximately proportional to the fourth root of eddy-current power loss in the target     

The Effect of DC Bias Conditions on Ferrite Core Losses

In switched-mode power supplies - the predominant type of power converter in contemporary electronic equipment - ferrite magnetic components under dc bias conditions are typically large and have relatively high losses. The nature of these losses is not widely understood, and research in this area has been hampered by the difficulty of obtaining accurate core loss measurements. This paper reviews previous studies on the nature of core losses under dc bias, and presents new results, measured by a technique that has not previously been utilized for the measurement of core losses under dc bias conditions. The results show that ferrite core losses increase significantly with an increasing dc bias, and highlight the need for further research over a wider range of conditions to fully characterize the phenomenon.     

A multi-objective GRASP procedure for reactive power compensation planning

A multi-objective approach based on the GRASP (Greedy Randomized Adaptive Search Procedure) meta-heuristic is proposed to provide decision support in the problem of locating and sizing capacitors for reactive power compensation in electrical radial distribution networks. The installation of capacitors (local sources of reactive power) in the network is aimed at correcting the power factor to improve the quality of service, particularly the network voltage profile, and reduce energy losses and power peak. The mathematical model explicitly considers two conflicting objective functions: the minimization of the network active losses and the minimization of the capacitor installation cost. An algorithmic approach based on GRASP is presented for the characterization of the non-dominated solution set.     

Measurement of losses and saturated permeability of saturable coresunder submicrosecond saturation

Two specific methods are introduced for obtaining accurate losses and saturated permeability of saturable cores under submicrosecond saturation. One employs an additional inductor for accurate measurement of the losses. The other minimizes stray inductance for accurate measurement of the saturated permeability. The measured relative permeability of Co-based amorphous cores rapidly drops to nearly 1.0. On the other hand, ferrite cores need a much larger magnetic field than that for Co-based amorphous cores in order to obtain the relative permeability of 1.0     

Nickel–zinc ferrite fabricated by sol–gel route and application in high-temperature superconducting magnetic energy storage for voltage sag solving

Ni–Zn ferrite nanoparticles of well controlled electromagnetic properties can be obtained through some chemical methods. In this study, the fine particles of Ni–Zn ferrite were prepared and fabricated using sol–gel route at low and high temperatures. The results gathered from the X-ray diffraction (XRD) indicated the amount of single-phase spinel ferrite constituents could be formed at a temperature below 400 °C. The Fourier transform-infrared spectroscopic (FT-IR) and the analyses using the microscopic photomicrographs were used to identify the formation of Ni–Zn spinel ferrite. The initial magnetic permeability showed that the inductance of the fabricated ferrite cores was of the highest value. Therefore, a laboratory coil equipped with a high-temperature superconducting magnetic energy storage (HT-SMES) was designed. The theoretical analysis of the torus with rectangular shaped coils was also carried out, and for this, a consideration for the average magnetic field inside the torus was used to calculate the inductance of the shape. Using uninterruptible power supply (UPS) and power conditioning system (PCS) which give details of the application of μ-SMES in solving voltage sag, a schematic diagram is also reported.     

Geometrical factors affecting magnetic properties of wound toroidalcores

Although toroidal cores wound from grain-oriented silicon iron strip are basically simple devices used in many applications, their magnetic properties are known to vary in a complex manner with core dimensions. The theoretical effects of radial magnetic field and flux density variation, interlamina normal flux, and winding stress on the real and apparent power loss and the permeability of a range of toroids with typical commercial dimensions are discussed. Comparisons are made with actual performance. It is shown that the radial variation of flux densities has a very small effect on the power loss and permeability but the interlamina normal flux has an influential effect, particularly in small-diameter toroids. It is shown that to obtain low losses and magnetizing currents, toroids should be designed using wide strips having large internal diameter and low buildup     

Unusual Effects Measured Under DC Bias Conditions on MnZn Ferrite Material

Switch mode power supplies are the predominant form through which power conversion is currently implemented in electronic equipment. Within such power supplies, ferrite cored magnetic components are commonly placed under dc bias conditions which, due to magnetomechanical effects, can result in higher than expected core losses. This paper presents measurements that show the impact of magnetomechanical effects on the losses of a MnZn ferrite core material under low ac excitation and high dc bias conditions. The measurements are made using an accurate measurement circuit, and the results show the impact on losses of magnetomechanical resonance. In addition distorted, figure-eight shaped $Bhbox{-}H$ loops are measured, which are also believed to manifest from magnetomechanical interactions. These $Bhbox{-}H$ loops show that, on a transient basis, magnetomechanical interactions may take place in a manner that is not only lossless, but returns energy back to the excitation supply.      

Synthesis and characterization of magnetic and microwave absorbing properties in polycrystalline cobalt zinc ferrite (Co<Subscript>0.5</Subscript>Zn<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>) composite

In this research work, magnetic and microwave absorption loss and other response characteristics in cobalt zinc ferrite composite has been studied. Cobalt zinc ferrite with the composition of Co_0.5Zn_0.5Fe₂O₄ was prepared via high energy ball milling followed by sintering. Phase characteristics of the as-prepared sample by using XRD analysis shows evidently that a high crystalline ferrite has been formed with the assists of thermal energy by sintering at 1250 °C which subsequently changes the magnetic properties of the ferrite. A high magnetic permeability and losses was obtained from ferrite with zinc content. Zn substitution into cobalt ferrite has altered the cation distribution between A and B sites in spinel ferrite which contributed to higher magnetic properties. Specifically, Co_0.5Zn_0.5Fe₂O₄ provides electromagnetic wave absorption characteristics. It was found that cobalt zinc ferrite sample is highly potential for microwave absorber which showed the highest reflection loss (RL) value of ??24.5 dB at 8.6 GHz. This material can potentially minimize EMI interferences in the measured frequency range, and was therefore used as fillers in the prepared composite that is applied for microwave absorbing material.     

Numerical Modeling of Growth Kinetics of Pro-eutectoid Ferrite Transformed from Austenite in Fe-C-∑X Alloys

In the present paper, a numerical modeling was developed to simulate the growth kinetics of ferrite transformed from austenite in Fe-C-∑X (X denotes substitution elements, such as Mn, Ni, Cr etc.) steels by solving the diffusion equation using finite difference method (FDM). Coupled with the kinetic modeling, thermodynamic calculations were carried out to determine the γ/α phase equilibrium conditions using a para-equilibrium (PE) model. The dissipation of free energy for γ→α phase transformation due to the so-called solute drag effect (SDE) was taken into account in the thermodynamic modeling. With this modeling, simulations on the growth kinetics of ferrite in the steels containing austenite-stabilizing and ferrite-stabilizing elements (such as Ni, Mn and Si, Cr, respectively) were performed, which indicates that it deviates from the parabolic growth rate law after the initial stage of transformation. The results were compared with the experimental values given by Bradley and Aaronson, showing that this model has a reasonably good accuracy to predict the growth kinetics of ferrite.     

Core-shell structured Mn-Zn-Fe ferrite/Fe-Si-Cr particles for magnetic composite cores with low loss

A Mn-Zn-Fe ferrite layer, several hundred nanometers thick, was deposited on the surface of Fe-3.5Si-4.5Cr (mass%) powder particles as an insulating material by an ultrasonic enhanced ferrite plating method. The compositions of the Mn-Zn-Fe ferrite layer were Mn_0.18Zn_0.27Fe_2.55O₄, Mn_0.38Zn_0.25Fe_2.37O₄, and Mn_0.54Zn_0.24Fe_2.22O₄. The core loss (P_cv) performances of the compacted cores and magnetic properties of the core-shell structured powders were evaluated. All the ferrite-coated cores exhibited a saturation flux density (B_s) in the range of 1.54–1.56?T derived from their soft magnetic metal and ferrite composition. All ferrite-coated cores annealed at 773?K exhibited a constant permeability µ′ in the frequency range up to 50?MHz owing to the insulating effect of the ferrite layer, and the Mn_0.54Zn_0.24Fe_2.22O₄ ferrite-coated core exhibited the highest real permeability µ′ of 56 at 50?MHz. The core loss of the Mn-Zn-Fe ferrite-coated Fe-3.5Si-4.5Cr cores was 604–738?kW/m³ at 100?kHz and 50?mT, which was much smaller than that obtained for the Fe-3.5Si-4.5Cr core without a ferrite layer (3617?kW/m³). The eddy-current loss (P_e) of the Mn-Zn-Fe ferrite-coated Fe-3.5Si-4.5Cr cores considerably decreased compared with those of the non-coated Fe-3.5Si-4.5Cr core owing to the insulating properties of the ferrite layer.     

Kinetics and microstructural modeling of isothermal austenite-to-ferrite transformation in Fe-C-Mn-Si steels

During the multi-stage processing of advanced high-strength steels, the austenite-to-ferrite transformation, generally as a precursor of the formation of other non-equilibrium or metastable structures, has a severe effect on the subsequent phase transformations. Herein, a more flexible kinetic and microstructural predictive modeling for the key austenite-to-ferrite transformation of Fe-C-Mn-Si steels was developed, in combination with the classical nucleation theory, the general mixed-mode growth model based on Gibbs energy balance, the microstructural path method and the kinetic framework for grain boundary nucleation. Adopting a bounded, extended matrix space corresponding to a single ferrite grain, both soft-impingement and hard-impingement can be naturally included in the current modeling. Accordingly, this model outputs the ferrite volume fraction, the austenite/ferrite interface area per unit volume, and the average grain size of ferrite, which will serve as the input parameters for modeling the subsequent bainite or martensite transformations. Applying the model, this work successfully predicts the experiment measurement of the isothermal austenite-to-ferrite transformation in Fe-0.17C-0.91Mn-1.03Si (wt%) steel at different temperatures and explains why the final-state average grain size of ferrite has a maximum at the moderate annealing temperature. Effectiveness and advantages of the present model are discussed arising from kinetics and thermodynamics accompanied with nucleation, growth and impingement.     

Unusual high-frequency behavior of some amorphous metallic-alloy tape-wound magnetic cores

The behavior of several samples of amorphous metallic-alloy tape-wound magnetic cores excited under sine-wave voltage conditions in the 1 kHz to 100 kHz frequency range is investigated. These tape-wound cores made by Magnetics, Inc. from two different Allied Corporation amorphous metallic-glass alloys, METGLAS® alloy 2605S-3 (composition Fe79B16Si5) and METGLAS® alloy 2605SC (composition Fe81B13.5Si3.5C2), are studied along with Magnetics, Inc. F ferrite cores. Measurements of the induced-voltage and exciting-current waveforms are used to obtain dynamic (ac) core characteristic loops of flux density B versus net ampere turns per unit magnetic path length Npip/lm, as well as core loss. The behavior of one of the amorphous metallic-glass alloys (Alloy 2605S-3) at flux-density levels in the range of 0.5 T and 1 T is found to lead to core characteristic loops with strange shapes and to unusual variations in the plots of energy loss per unit volume per cycle versus frequency. The second amorphous alloy (Alloy 2605SC) shows similar unusual properties but only at high flux-density levels close to saturation, above 1.25 T. The unexpected behavior observed in these two alloys is due to magnetoelastic resonances of the toroidally shaped cores. By modeling the tape-wound core as a thin ring, calculations are made for the resonant frequencies corresponding to the mode of extensional vibrations which agree well with experimentally measured results.     

Stress relaxation phenomena in NiCuZn ferrites induced by annealing

The present study deals with the detection and correlation of the stress relaxation phenomena that are induced in NiCuZn ferrites, as an effect of an additional annealing process that takes place after sintering. The effect of annealing on the magnetic permeability and losses of NiCuZn ferrite materials is investigated and the microstructural changes of the samples are examined by transmission electron microscopy. The ferrite specimens were synthesized by the conventional ceramic method. Sintering temperatures between 1025 and 1100 °C were applied and the sintered samples were further annealed at temperatures 50 °C lower than the sintering ones. Results revealed an improvement of the power losses at low frequencies (50 kHz), while at the high frequency range (1 MHz) the relative loss factors increased. These results were in agreement with the detected microstructural changes in the polycrystalline microstructure that occurred due to the annealing process. The relation between the annealed microstructure, the specific resistivity and the magnetic losses of the NiCuZn ferrites specimens is discussed. It appears that the stress relaxation mechanism induced by annealing is attributed to the elimination of grain dislocations, which justifies the decrease of the specific resistivity of the specimens. The stress relaxation contributes to a reduction of the low frequency hysteresis losses while the decrease of the resistivity to an increase of the high frequency eddy current losses.     

High-Frequency Tunneling Magnetic Loss in Soft Ferrites

This paper considers high-frequency (200 kHz-1.0 MHz) losses in MnZn power ferrites and shows that none of the three well-known magnetic loss mechanisms (namely, hysteresis, classical eddy-current loss, and excess eddy-current loss) can account for the experimentally observed dependence of the loss on the frequency and flux density. In order to investigate the origin of this discrepancy, the electric field that is induced in the typical core when the material is driven at high frequencies and flux densities was estimated. The estimates show that these electric fields can be quite large. The paper presents experimental data on the electrical conductivity for such large electric fields, which shows a highly nonlinear behavior that can give rise to a modified eddy-current loss mechanism. By a simple curve fit to the nonlinear conductivity, the experimentally observed flux density dependence of the high-frequency loss, which previously could not be explained, can be reproduced by using this modified eddy-current loss mechanism. A modified ferrite structure can eliminate most of these extra losses by reducing the electric field generated at the grain boundaries due to high frequencies and flux densities     

Problems in the design of power transformers

The power loss of transformer cores can still be considerably reduced by improved joint design based on new knowledge of the localized flux distribution, both in the corners and in the limbs. Rotational flux has been measured in the T-joints of experimental cores, and it has been found to cause localized high loss regions dependent on the joint design. Circulating harmonic fluxes have been found in individual laminations in the limbs of three-phase cores. The path of the harmonics is independent of joint design although their magnitudes are dependent. Circulating 3rd harmonics as large as 0.3 T have been found in a core magnetized sinusoidally at 1.6 T. These cause additional losses calculated to be 20% of the nominal core loss, and great savings would be possible if the circulating harmonics could be reduced or eliminated.     

Alternating electromagnetic field computation in laminated cores

A finite element method is developed to compute alternating electromagnetic fields in laminated cores. The method is applied to a simplified model problem in order to evaluate power losses in mitered overlap joints. The influence of eddy currents on the magnetic field distribution in the neighborhood of the mitered joints is discussed. The power losses ate evaluated for cores with different overlap lengths.     

高频MnZn功率铁氧体研究进展

Mn Zn铁氧体因具有高磁导率、高饱和磁通密度、低损耗而成为高频磁性元件的首选材料,其高频损耗的降低对开关电源的小型化和高效化有重要影响。介绍了高频Mn Zn铁氧体材料的损耗构成和控制机理,总结了国内外高频Mn Zn铁氧体材料研究和开发的发展现状,并对高频Mn Zn铁氧体材料的发展前景进行了展望。     

Temperature-stable low-noise ferrite memory cores

Temperature-stable low-noise memory cores made from the substituted lithium and nickel ferrites were studied. Ferrite compositions which are suitable for miniature cores have been developed by studying magnetic properties of the ferrite in the system Li-M-M' and Ni-M-M' ferrite (M:Mn, Fe, Co, Ni, Cu, and Zn). Technological approaches for fabricating small memory cores were made by studying the effect of ferrite-powder parameters and sintering conditions on magnetic properties of the substituted ferrites. Typical pulse characteristics taken with coincident current mode for cores of 0.48, 0.32, and 0.27 mm φ OD are presented. It was found that the Ni-Mn-F(II) ferrites are suitable for a low-drive high signal-to-noise ratio (dV1/dVz) temperature-stable memory core.     

活性炭负载Co0.8Zn0.2Fe2O4铁氧体的制备及电磁性能研究

采用溶胶-凝胶法制备活性炭负载纳米钴锌铁氧体复合吸波材料研究。以柠檬酸为络合剂制备Co0.8Zn0.2Fe2O4铁氧体溶胶,加入活性炭于溶胶中,经浓缩制得活性炭/钴锌铁氧体凝胶,再经过低温煅烧,制备出形态和结构理想的活性炭负载钴锌铁氧体复合材料;详细地考察烧结温度、煅烧时间及活性炭与铁氧体的配比等工艺参数对复合材料的形态和结构的影响;分别采用X射线衍射(XRD)、扫描电镜(SEM)和能量散射X射线荧光光谱(EDX)对制备出的复合材料进行形貌、结构及组成表征分析。采用波导法在8.2～12.4GHz波段对活性炭负载纳米钴锌铁氧体复合材料进行电磁参数测试分析,结果表明所制备活性炭负载纳米钴锌铁氧体复合材料具有较高的电、磁损耗角正切值,其吸波性能较好。     

Design and identification of an equivalent circuit for an LCT component: inventory and representation of losses

A new kind of passive component, the LCT [integrated inductor (L), capacitor (C), and transformer (T)] is becoming very fashionable in the switch mode power supply area. Starting from our knowledge in transformer characterization, we recently elaborated an equivalent circuit for this component. This equivalent circuit is fully deducible from impedance measurements. No dismounting of the component is needed, and no information about its internal design is required. This paper aims mainly to present the new equivalent circuit and the method leading to its identification using a commercial impedance analyzer. The LCT intended to a 300-W power supply working at 200 kHz has been built and characterized between 100 Hz and 40 MHz. Analyzing the frequency dependence of the real part of serial and parallel impedances, several kind of losses rarely taken into account have been identified. Among these losses are those related to the capacitor insulator and those due to the dielectric constant of Mn-Zn ferrite core. Equivalent circuits are supplied to represent every type of loss, and their accuracy is checked.