Ferrite Losses Research Articles

高周波域における MnZn フェライトの損失について

To improve the core loss of MnZn ferrite at high frequencies,the loss characteristics were investigated. For a core with fine grains sintered at a low temperature, high density was obtained and the rapid increase in the loss factor at high frequencies was reduced. Numerical analysis was performed to divide the core loss into the hysteresis loss,the eddy current loss, the dielectric loss, and the residual loss. The residual loss was dominant at higher frequencies and decreased more for the core with a smaller grain size.

Analysis of eddy current loss in Mn-Zn ferrites for power supplies

An attempt was made to divide power loss in Mn-Zn ferrites into hysteresis loss, eddy current loss and residual loss factors experimentally. We noticed the correspondence between the temperature, Tmin at which hysteresis loss exhibits minimum value, and secondary peak temperature of initial permeability. Analyzing the power loss and electrical resistivity measured at Tmin, it was found that the powerless can be divided into hysteresis loss, resistivity dependent loss component (eddy current loss) and resistivity independent loss component. Consequently, the residual loss was identified to be a loss component independent of resistivity.

ＭｎＭｇＺｎフェライトの磁気損失について

The effects of the both grain size of a sintered body and the oxidation state of Fe ions on hysteresis loss of MnMgZn ferrite were studied in order to achieve low core loss. It is shown that grain growth is effective for achieving low hysteresis loss, but that the hysteresis loss falls to a minimum at an average grain size of 4μm. High temperature firing leads not only to grain growth but also to a reduction in number Fe3+ ions. It is thought that an appropriate number of Fe2+ ions lowers the magnetic anisotropy and results in low hysteresis loss. Mn2O3 addition and low oxygen partial pressure during the cooling state are effective for reducing core loss.

Computing ferrite core losses at high frequency by finite elements method including temperature influence

A finite elements method coupled with the Preisach model of hysteresis is used to compute the ferrite losses in medium power transformers (10-60 kVA) working at relatively high frequencies (20-60 kHz) and with an excitation level of about 0.3 Tesla. The dynamic evolution of the permeability is taken into account. The simple and doubly cubic spline functions are used to account for temperature effects respectively on electric and on magnetic parameters of the ferrite cores. The results are compared with test data obtained with 3C8 and B50 ferrites at different frequencies. >

Magnetic properties and the grain boundary structure of Mn-Zn ferrites with the addition of Nb 2O 5

The effects of the addition of Nb 2O 5 on the power losses in manganese-zinc ferrites have been investigated by measuring the magnetic properties and observing the grain boundary structures. The addition of Nb decreases the initial permeability and raises the resonance frequency. Power losses were analyzed as the sum of the contributions of hysteresis loss, eddy current loss and residual loss. The hysteresis and eddy current losses were reduced by about 10% by the addition of Nb below 200 kHz, in spite of the smaller magnetic permeability. These losses are thought to originate from the additive effect of Nb atoms, which are enriched in grain boundaries to form a high-resistivity layer and prevent Ca and Si atoms being incorporated with the spinel lattice. The residual losses were greatly reduced by the addition of Nb at higher frequencies. The origin of the difference in the residual losses is discussed.

Effect of ferrite morphology on fracture mode of stainless steel weld metal

Summary On the basis of stereographic fractographic observations, this paper describes an investigation of the relationship between the ferrite morphology and fracture mode of Fe‐18Cr‐8Ni stainless steel weld metal at cryogenic temperature and proposes a way of improving the weld metal toughness. A new etching technique is first used to observe the three‐dimensional ferrite morphology. This involves preferential dissolution of the austenite matrix at a specific potential using a potentiostat. The electrical potential used was ‐0.15 V vs an HgCl electrode. The technique is then applied for fractographic observations of fracture surfaces at cryogenic temperature. The results suggest that the cleavage fracture initiated at the continuous film‐like ferrite causes loss of fracture toughness. The austenite matrix containing globular or discontinuous vermicular ferrite, however, shows a dimple fracture pattern.

Comparison between the Kittel and Polder resonances in polycrystalline ferrites

Kittel and Polder resonance parameters in polycrystalline ferrite spheres have been determined simultaneously using the perturbation theory. Measurements were made with the same sample in order to establish a proper comparison between the Kittel and Polder parameters. The meaning of the shift of the ferromagnetic resonance field and the different parameters used to characterize the resonance losses in polycrystalline ferrites are discussed. Discrepancies between the Kittel and Polder parameters are explained by studying the dependence of the linewidth and the ferromagnetic resonance field on the applied field. There is good agreement between the experimental results and the theoretical predictions. >

Effect of sintering parameters on Zn loss for preparation of high permeability MnZn ferrites

The significant effects of sintering atmosphere and setter materials on the zinc loss of Mn-Zn ferrites are shown. It is demonstrated that the zinc loss will reduce the initial permeability from 11000 to 6000. The key sintering parameters increasing this zinc loss are low oxygen atmosphere in high temperature, high gas flow rate in the furnace, and the reaction of zinc oxide with Al/sub 2/O/sub 3/. Minimizing zinc loss during sintering is of paramount importance to the successful preparation of high permeability Mn-Zn ferrites.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of PbO-B/sub 2/O/sub 3/-SiO/sub 2/ glass on preparation of low loss Mn-Zn ferrites

Low power loss manganese zinc ferrites conventional process have been studied by addition of CaO and glasses. It was found that addition of CaO and PbO-B/sub 2/O/sub 3/-SiO/sub 2/ at the same time can effectively reduce the power loss of Mn-Zn ferrites. The glasses improve the sinterability of Mn-Zn ferrites, and good magnetic properties can be obtained by sintering at relatively low temperatures under air atmosphere. The ferrites with CaO additions only cannot be sintered very well at low temperatures and the sintered density is about 4.5 g/cm/sup 3/. Higher sintered density (>4.7 g/cm/sup 3/) and saturation magnetization (4600 Gauss) can be achieved by cooperative addition of CaO and PbO-B/sub 2/-O/sub 3/-SiO/sub 2/ glass sintered at 1170 degrees C. The optimum power loss, 250 kW/m/sup 3/ at 500 kHz, is reasonably good for conventional processing.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ferrite core loss for power magnetic components design

A practical method is presented for computing high-frequency ferrite core losses in the magnetic component for arbitrary voltage waveforms. The model presented requires only a few material parameters as input. To calculate ferrite hysteresis losses, a model based on empirical rules is employed. For high-frequency eddy current losses, a built phenomenon is assumed. It is demonstrated that the hysteresis model reproduces all of the important known features of the soft ferrites. These features include hysteresis loop shapes for low- and high-field excitations, the nonlinear permeability behavior, and hysteresis loss dependence on the amplitude of the exciting field. It is found that the total calculated core loss as a function of frequency and flux density correctly describes the observed soft ferrite behavior. The theoretical results are compared with available data for two commercial ferrites, and good agreement is found up to fairly high frequencies ( approximately 500 kHz). >

Magnetic losses in ferrites and nanocrystalline ribbons for power applications

The frequency and induction dependence of magnetic losses in Mn-Zn ferrites and in nanocrystalline alloys have been studied. At high frequencies (>100 kHz) the specific loss in power ferrites is remarkably lower than in the nanocrystalline material if induction values usually used in power supplies are applied.

The influence of atmosphere on hysteresis loss and eddy current loss of low loss Mn-Zn ferrites (abstract)

The working frequency of Mn-Zn ferrites in switching power supply has been increased recently. Therefore, the manufacturing Mn-Zn ferrites with low loss at high frequency is very important. However, there were few reports concerning the core loss of Mn-Zn ferrites.1 It is beneficial to study the parameters affecting the core loss of Mn-Zn ferrites. Therefore, we studied the influence of atmosphere on the hysteresis loss (Wh) and eddy current loss (We) for different compositions in this work. Three compositions, Mn0.70Zn0.21−xFe2.09+xO4 (x=0, 0.01, 0.02), were prepared by traditional ceramic process. The sintering condition is 1385 °C for 4 h. Then, the samples are annealed at 1100 °C for 24 h in different oxygen partial pressure (0.015–1.0 vol %). Experimental results show that both We and Wh have minimum value at different oxygen partial pressure for samples with different composition. Increasing Fe content which raises the Fe++ concentration shifts the We and Wh minimum point to higher annealing oxygen partial pressure. It is mainly due to the oxidation of Fe++ and the transition of conduction mechanism, and it will be further discussed later. We can obtain the lowest core loss for using 10 and 100 kHz are samples with composition x=0 annealed in 0.07 and 0.2 vol % oxygen partial pressure, respectively. Summarily, for application to low loss at different working frequency, it is found that different optimized atmosphere should be controlled during annealing for different composition.

Microstructure and physical properties of Mn-Zn ferrites for high-frequency power supplies

The power loss of Mn-Zn ferrites and its dependency on the microstructural factors have been investigated. The power loss was found to be lowered due to the formation of a high-electrical-resistive boundary layers, which is accomplished by an addition of specific refractory oxides, which are concentrated on the grain boundary and form a boundary layer with CaO. The new material, having a low power loss at high frequency (∼1 MHz), has been developed with the HfO2 addition.

Extremely low frequency losses and thermal fluctuation after effect in soft ferrites

Magnetic losses in soft magnetic ferrites have been measured at extremely low frequencies and high magnetic inductions. A logarithmic variation of losses per cycle with frequency has been found in a frequency range between 0.01 Hz and less than 100 Hz. This anomalous loss with frequency dependence is attributed to the thermal fluctuation after effect which yields the same anomalous losses in metallic soft magnetic materials. The after effect constant Sv has been calculated from this anomalous loss and the static and eddy current losses in soft ferrites have been discussed.

Microstructure and properties of Ni-Zn ferrites sintered from slip cast colloidally precipitated particles

The microstructural dependence of magnetic permeability and magnetic loss of Ni-Zn ferrites sintered from split-cast colloidally precipitated ultrafine particles was investigated. A low-loss Ni-Zn ferrite (tan delta / mu /sub 0/=4.92*10/sup -5/ at 1 MHz) having nearly maximum attainable density, fairly uniform and small grain size, and no significant zinc loss was prepared by sintering at 1100 degrees C. There was considerable discrepancy in the permeability-grain size relationship between ferrites sintered at <or=1100 degrees C and at >1100 degrees C. The zinc loss and intragranular pores in 1100 degrees C sintered ferrites may explain this discrepancy.<<ETX>>

Optimum design for WYE-junction circulator

Formulas for the eigenimpedance of YY-junction circulators are proposed. The eigenimpedance is used to find a circulator equation that satisfies the circulating conditions and a design procedure that differs from those based on admittance slope. Examples are given for calculating circulator characteristics by CAD or optimization methods, taking ferrite electromagnetic losses into account. >

Off resonance relaxation in hexagonal ferrites

The effective linewidth technique has been applied to study field dependent microwave losses in hexagonal ferrites for the first time. Data have been obtained on single crystal Zn 2-Y and ZnTi-M as well as oriented polycrystalline NiCo-W materials. The results clearly show that the high field effective linewidth is significantly lower than the ferromagnetic resonance (FMR) linewidth. This implies that inhomogeneity or two-magnon relaxation contributes significantly to the FMR linebroadening and that the intrinsic linewidth is much lower than the FMR linewidths. The results also demonstrate the usefulness of the effective linewidth technique to study microwave losses even under conditions where the actual FMR peak is inaccessible.

Comments on "Use of Ferrites for Absorption of Electromagnetic Waves"

It is shown that considerations of hysteresis losses in ferrites are not relevant to their performance as absorbers of radar signals.

Finite-Element Analysis of H-Plane Waveguide Junction with Arbitrarily Shaped Ferrite Post

A numerical approach for solving the problem of H-plane waveguide junctions with Iossy ferrite posts of arbitrary shape is proposed. The junctions are allowed to have arbitrary cross section. The approach is a combination of the finite-element method and the analytical method. To show the validity and usefulness of tbe method, Y-junction circulators with a circular ferrite post are considered. Our results agree well with earlier experimental and theoretical results. The performances of Y-junction circulators with a triangular equilateral ferrite post or a triangular ferrite post having depressed sides are investigated. The influences of the ferrite losses on the performance are examined.

High quality soft heating method utilizing temperature dependence of permeability and core loss of low Curie temperature Ferrite

High quality Soft Heating method utilizing low Curie temperature ferrite is developed. The heater generates sufficient heat at room temperature and stops heating abruptly an the Curie temperature. The heat characteristics of the heater and the suitable exciting conditions are clarified.