Mn-Zn Ferrite Core Research Articles

Loss Analysis of a Mn-Zn Ferrite Core with the Spatial Network Method Taking the Dynamic Magnetic Loss into Account

A circuit model was developed to analyze the electromagnetic field in ferrites, for contribution to the design of power circuits by taking into account the power loss in the high-frequency region. The ferrite power loss in the high-frequency region consists of the hysteresis loss and the dynamic magnetic loss. This paper proposes a novel model for electromagnetic field analysis, which is able to compute the magnetic, eddy current and displacement current losses, based on the spatial network method. The validity of the method is verified by comparing the computed power losses with those obtained by the finite element method.

Using a Single Toroidal Sample to Determine the Intrinsic Complex Permeability and Permittivity of Mn–Zn Ferrites

Analysis of the principle of the published lumped circuit methods for determination of the intrinsic complex permeability and permittivity of the Mn-Zn ferrites reveals that as long as the electric and the magnetic field distributions in the core(s) in two measurements are different, the two intrinsic values can be determined. Using this principle, we developed a set of general lumped circuit methods based on a toroidal Mn-Zn ferrite core as the measurement sample. We examined two possible different excitation modes: magnetic field excitation and electric field excitation. The two different excitation modes result in significantly different field distributions in the sample. Thus, high accuracy can be guaranteed in principle. For the magnetic field excitation, we present in this paper a general finite-difference method to solve the fields in the core and the impedance of the ferrite core inductor. To avoid the stray capacitance among the coils of the ferrite core winding inductor in the measurement, we made a set of short-ended coaxial test fixtures. We performed experiments to determine the intrinsic complex permeability and permittivity of a Mn-Zn ferrite core up to 10 MHz by using the two general methods and validated the measured intrinsic values experimentally.

Permeability enhancement by induced displacement current in magnetic material with high permittivity

Based on a analytical model, this paper reveals that instead of demagnetization, the induced displacement current in a Mn–Zn ferrite core due to its high permittivity can produce a magnetic field that effectively adds to the incident magnetic field in the low-loss frequency region. This leads to a resultant magnetic field being larger than incident field in magnitude, and results in measured permeability being higher than its intrinsic value in the low-loss frequency region. It is also found that such effect is more pronounced in large core than in small core. With increasing frequency and consequently the core being more lossy, the induced magnetic field due to both conductivity and imaginary part of complex permittivity demagnetize the magnetic material and counteracts the incident magnetic field. In consequence, the measured real part of complex permeability becomes smaller than its intrinsic value. The larger the core dimension, the smaller the real part of complex permeability is. These conclusions based on the numerical analysis are in good agreement with the experimental observation in the aspect of change tendency of permeability versus frequency.

An Efficient Finite-Difference-Based Newton–Raphson Method to Determine Intrinsic Complex Permeabilities and Permittivities for Mn–Zn Ferrites

This paper presents a fast and efficient algorithm, based on the finite-difference method, to extract intrinsic complex permeability and permittivity from measured values for Mn-Zn ferrite cores. Our algorithm is considerably more efficient than the analytical solution-based Newton-Raphson method and reduces computing time from hours to tens of seconds

Magnetic loss analysis in Mn–Zn ferrite cores

Magnetic losses have been measured and analyzed upon a wide range of frequencies in Mn–Zn ferrite ring cores. Exploiting the concept of loss separation and modeling the conductivity process in the heterogeneous material as a function of frequency, the role of the different energy dissipation mechanisms has been elucidated. It is shown, in particular, that eddy current effects can be appreciated, in standard materials and cores, only on approaching and overcoming the MHz range. The basic mechanism for hysteresis and low-frequency losses is therefore identified with the domain wall relaxation engendered by spin damping processes. Resonant absorption of energy associated with magnetization rotation is in turn deemed to chiefly contribute to the loss upon the practical range of frequencies going from a few 10 4 Hz to a few MHz.

低温焼結ＭｎＺｎフェライトの磁気特性と磁化過程

Magnetic properties and magnetization process of MnZn ferrite cores by low temperature sintering were investigated. The powder was prepared using the conventional ball milling. The specimens were sintered at 900°C for 5 houres in reductive atomosphere including CO2 and H2. The flow rate H2/CO2 was the best between 1 and 2%. The initial permeability was 2379 at 100kHz, 0.5V.Magnetization process was observed by Bitter method. Wide width magnetic domains (180°domain) were easier magnetized than narrow one. On the other hand, 90°domains did not change the width with increasing magnetic field.

低温焼結ＭｎＺｎフェライトの磁気特性と磁区構造

Magnetic properties and magnetic domains of MnZn ferrite cores by low temperature sintering were investigated. The powder was prepared using the conventional ball milling. The specimens were sintered at 900°C for 5 hours in reductive atmosphere. Grain growth of sintered cores got remarkable by adding above 0.05 wt% meta-boric lithium (LiBO2). The initial permeability including 0.05wt%LiBO2 was 2071. Magnetic domains were investigated by Laser microscope and SEM using magnetic colloid. Width of magnetic domains were smaller than a commercial MnZn high permeability core (Material spec. is 15000 at 10kHz). It was suggested that this core has compressive stress by magnetic domain observation.

A new wideband common-mode noise filter consisting of Mn-Zn ferrite core and copper/polyimide tape wound coil

A new wideband common-mode noise filter for switching power supplies has been developed. The filter consisted of an Mn-Zn ferrite core and a copper/polyimide tape wound coil. The tape wound coil had two signal lines, two ground lines, and a polyimide dielectric film. The filter exhibited a common-mode rejection of over 30 dB in the wide frequency range of 100 kHz to 100 MHz. The wideband common-mode filtering was due to the high-frequency magnetic loss of the Mn-Zn ferrite core and the optimum ground point selection for the ground lines.

Synchronous rectification for contactless power supply utilizing Mn–Zn ferrite core coils

Contactless power supply systems transmit electric power by electromagnetic induction with a pair of coils. The efficiency and the output voltage depend on parameters of coils. We studied the best parameter values that realize stable high efficiency contactless power supply. In the application with low output voltage, the voltage drop of the diodes becomes dominant power loss. A synchronous rectification was proposed as a solution of this problem. Our contactless power supply system for an artificial heart operates at 190kHz. We use planar coils with Mn–Zn ferrite cores. Highly stable output voltage and 88% maximum efficiency were realized.

A practical method to determine intrinsic complex permeabilities and permittivities for Mn-Zn ferrites

Mn-Zn ferrite cores present high permeability within the kilohertz-to-megahertz frequency range. They also present high permittivities within the same frequency range. High permeabilities lead to significant permittivity measurement errors when the conventional two-parallel-electrode method is used. In contrast, high permittivities result in the deviations of measured permeabilities from their intrinsic values. This paper presents a field-circuit coupled method to study each of these two phenomena by examining a ferrite toroid with rectangular cross section. The same toroid is used to construct an inductor and a capacitor, respectively. Analytical expressions for electric and magnetic fields in, and complex power supplied to the inductor and capacitor are formulated. Results are obtained, which show that the measured permeabilities and permittivities for Mn-Zn ferrites deviate from their intrinsic values significantly. A Newton-Raphson method is then introduced to determine the intrinsic permeabilities and permittivities based on their measured values.

Effect of High Permeability on the Accurate Determination of Permittivity for Mn–Zn Ferrite Cores

This work presents a field-circuit-coupled method to investigate differences between intrinsic and measured permittivities for a Mn-Zn ferrite. Electric and magnetic fields in a flat cylindrical ferrite, which is used here to construct a ferrite capacitor, are solved analytically. Then, complex power supplied to the capacitor is calculated. On the basis of the complex power, parameters in an equivalent circuit for the ferrite capacitor are extracted. The paper examines the validity of the developed mathematical model. Numerical results show that for a ferrite with high permeabilities, measured permittivities follow intrinsic values well at low frequency but fail to embody the intrinsic values when the frequency runs above several hundred kilohertz. Numerical results also demonstrate that the dimensions of the sample under investigation play a role in measurement errors. The larger the radius of the cylindrical ferrite is, the higher the errors are. Correction curves are generated, from which the measured permittivities can be corrected to reflect the intrinsic values.

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.

Reducing Dielectric Losses in MnZn Ferrites by Adding<tex>$hboxTiO_2$</tex>and<tex>$hboxMoO_3$</tex>

We investigated the complementary effects of TiO/sub 2/ and MoO/sub 3/ additives on the magnetic properties, the core loss, and the dielectric properties of MnZn ferrites. We analyzed the composition factors influencing the permeability of MnZn ferrites. A high initial permeability base ZnO-MnO-Fe/sub 2/O/sub 3/ composition ratio was selected. Electrical and dielectric analyses indicated that the introduction of TiO/sub 2/ can improve the high-frequency loss properties of MnZn ferrite cores, but such introduction will also have a negative effect on the magnetic properties of the sintered samples. Introduction of MoO/sub 3/ can alleviate the negative influence of TiO/sub 2/ and also reduce the internal polarization intensity. As a result, the dielectric constant and corresponding dielectric loss may be reduced. We give experimental results in the paper.

Ｍｎ−Ｚｎフェライトを用いたスパイラル型伝送線路の特性解析

We developed spiral-type transmission line device consisting of a spiral winding with a polyimide dielectric film, a ground plane, and a Mn-Zn ferrite pot core. To analyze the transmission characteristics of the devices, we introduced a coupled distributed constant circuit model. Differential equations for voltage and current obtained from the analysis model include impedance and admittance matrixes representing electromagnetic coupling between different turns. As a result, the calculated transmission characteristics agreed well with the measured ones.

Spiral-type transmission line with an Mn-Zn ferrite core

Spiral-type transmission-line devices using an Mn-Zn ferrite core were developed, which consisted of a spiral winding with a polyimide dielectric and a ground plane, an Mn-Zn ferrite pot core (TDK; PC-50). The devices exhibited 20-dB attenuation in a wideband frequency range, which was not only due to the high frequency loss of the ferrite but also due to the distributed constant circuit operation. To analyze the characteristics, a distributed constant circuit model was introduced considering magnetic coupling between different turns in the spiral winding.

Magnetic properties and mechanical strength of MnZn ferrite

From MnZn ferrite ("6H20" of FDK production), cores having grain size of about 8/spl sim/10 /spl mu/m were produced by controlling the calcination temperature, after-calcination milling time, and sintering conditions. The ferrite powder production conditions and core microstructure were examined to determine their effects on the magnetic properties and mechanical strength of MnZn ferrite cores. A tendency of core loss to decline with a decrease in grain size was confirmed. Strength increased also with a decrease in grain size. Thus, a relation similar to that between strength and fracture toughness in the equation of Griffith-Irwin was noted. By these findings, it has become possible to produce MnZn ferrite cores with lower loss and greater strength.

Estimation of MnZn ferrite core losses in magnetic components at high frequency

This paper deals with a magnetic modeling for the estimation of the dynamic losses in soft ferrite cores. A time-domain MSPM based algorithm for the hysteresis losses evaluation, added to a simplified, one-dimensional modeling of the eddy current losses, are used to predict the total specific losses in cores subjected to a.c. and distorted wave-forms. Experimental analysis show satisfactory capability of prediction of the modeling proposed, used as a CAD tool.

微結晶Ｍｎ‐Ｚｎフェライトを用いた伝送線路トランスの試作

A novel high-frequency transformer using a fine-grain Mn-Zn ferrite has been proposed for transmission line use. The device consists of a fine-grain Mn-Zn ferrite core, polyimide film, copper planar spiral winding, and copper ground-plane, which operate as a distributed constant circuit. A quarter-wavelength transmission-line transformer with a large voltage-gain under higher impedance termination has been investigated, and it has been applied to a step-up transformer in a high-frequency inverter for a cold fluorescent lamp (CFL).

Effects of multi-segment structure on core losses in MnZn ferrites at high frequencies

Multi-segment cores have been developed by cutting standard MnZn ferrite cores into thin segments and then re-assembling the segments together. All the segments were separated by a thin film of air or insulation materials of microscopic dimensions. The core loss properties of these experimental samples have been investigated between the frequencies of 200 kHz to 2 MHz. The real and imaginary parts of the effective permeability have been determined from these measurements. Experiment results show that the multi-segment ferrite cores are effective in reducing the core loss by possible mechanisms of reduction in the internal electromagnetic field strength and of reduction in the influence of the magnetic skin effect.

Preparation of phase homogeneous Mn–Zn ferrite powder by spray pyrolysis

Two kinds of aqueous precursor solutions are used to synthesize Mn–Zn ferrite powders: (i) nitrate (NO) precursor—derived from solutions of Mn(NO3)2, Zn(NO3)2, and Fe(NO3)3; and (ii) acetate (AC) precursor—derived from solutions of Mn(CH3COO)2, Zn(CH3COO)2, and Fe(NO3)3. The composition of the powders synthesized from the precursor AC is very uniform, whereas powders derived from the precursor NO have Mn and Zn segregated on the particle surfaces. In addition, the powders synthesized from precursor AC are solid spherical particles with fine porosity, whereas many hollow and fragmented particles are observed in the powder derived from precursor NO. Overall, the properties of Mn–Zn ferrite cores prepared from the precursor AC are superior to those prepared from the precursor NO. The reasons for the differences are explained and described in detail. The AC precursor powders synthesized by spray pyrolysis produced Mn–Zn ferrite cores with good magnetic properties.