General Properties of Low-frequency Power Losses in Fe-based Nanocrystalline Soft Magnetic Alloys

The dependences of the power loss per cycle on frequency f and amplitude flux density Bm have been investigated for the three main original magnetic states in five sorts of Fe-based nanocrystalline soft magnetic alloys in the ranges of 10 Hz<=f<=1000 Hz and 0.4 T<= Bm <=1.0 T. The total loss P is decomposed into the sum of the hysteresis loss Physt, the classical eddy current loss Pel and the excess loss Pexc. Physt has been found to be proportional to Bm^2 and f. The behavior of Pexc/f vs f being equivalent to P/f vs f clearly exhibits nonlinearity in the range not more than about 120 Hz, whereas the behavior of P/f vs f roughly shows linearity in the range far above 100 Hz and not more than 1000 Hz. In the range up to 1000 Hz, Physt is dominant in the original high permeability state and the state of low residual flux density, whereas Pexc in the state of high residual flux density is dominant in the wider range above about 100 Hz. The framework of the statistical theory of power loss has been used for representing the behavior of Pexc/f vs f. It has been found that the number n of the simultaneously active 'Magnetic Objects' linearly varies as n = n0 + Hexc/H0 as a function of the dynamic field Hexc in the range below about 120 Hz, whereas n approximately follows a law of the form n = n0 + (Hexc/H0)^m with 1 < m < 2 in the range far above 100 Hz and not more than 1000 Hz. The values of the field HO in principle related to the microstructure and the domain structure have been calculated for the three states.

Calculation of Skin Depths and Eddy-Current Power Losses for Magnetic Position Sensors

We present a theoretic model to calculate skin depths and eddy-current power losses for a magnetic position sensor. Eddy-current, arised from the operation of an alternating-current excitation, induces secondary currents and fields between magnetic material and magnetic position sensor. In this paper, a magnetic position sensor system is simplified to be an outer-winding coil along the axial direction of a low carbon steel bar. The analytical model is derived from basic field and circuit theory considering a linear approximation for a nonlinear permeability. Thus the skin depths and eddy-current power losses from the model in eddy-current modeling techniques at various frequencies of an excited current source can be calculated. The proposed configuration is capable of predicting the skin depths and eddy-current power losses for a magnetic position sensor and has a consistence with experiments.

Hysteresis loss free soft magnetic ferrites based on Larmor precession

A big enough transverse magnetic field applied to soft magnetic ferrite toroid can magnetize the ferrite to a saturation level in transverse direction and almost completely suppresses magnetic domain structures in the ferrite,the response to the longitudinal alternating electromagnetic field changes from the original domain wall displacements and spin rotations to the precession of magnetization around the transverse field,and the hysteresis loss disappears in the ferrites.Both theoretical and experimental results indicate that the permeability and magnetic loss in the ferrite can be controlled by adjusting the transverse magnetic field.A higher Q value with relatively low permeability can be achieved by increasing the transverse field,which ensures that the ferrite can be operated at high frequencies,with magnetic loss being very low.

Influential Factors on Electromagnetic Properties of Selected 3D Reticulated Ceramics

3D reticulated ceramics (3DRCs) with the composition containing SrFe12O19-SiC-TiO2 were prepared by a replication process with polyurethane sponges as the template in ceramic slurry. The electrical conductivity, dielectric and magnetic parameters of 3D reticulated ceramics (3DRCs) were measured with changes in cell size of the sponges, contents in the slurry and sintering temperature in this paper. Discussions about the influential factors of those parameters were focused on their electrical conductivity. The experimental results indicated that the electrical conductivity of 3DRCs raised with the increase of cell size, SiC/SrO 6Fe2O3 with weight ratio and sintering temperature. X-ray diffractions and SEM were used to investigate the relationship between electrical conductivity and sintering temperature. Deoxidizing reactions of SrO 6Fe2O3 caused the increasing electrical conductivity. The real part of permittivity (ε') and imaginary part of permeability (μ') raised with the increase of electrical conductivity (σ). The imaginary part of permittivity (ε') has a maximum at 10o S/cm with the increase of a, and the real part of permeability (μ') changes slightly with the increase of a. When a is at the range of 10-4 S/cm to 10o S/cm (a semi conductive state), both the imagine part of permittivity and permeability raises with increasing a, therefore, the 3DRCs present their high electromagnetic loss properties.

Effects of the Mn/Co ratio on the magnetic transition and magnetocaloric properties of Mn_(1+x)Co_(1-x)Ge alloys

We have investigated the magnetic transition and magnetocaloric effects of Mn1＋xCo1-xGe alloys by tuning the ratio of Mn/Co. With increasing Mn content, a series of first-order magnetostructural transitions from ferromagnetic to paramagnetic states with large changes of magnetization are observed at room temperature. Further increasing the content of Mn （x = 0.11） gives rise to a single second-order magnetic transition. Interestingly, large low-field magnetic entropy changes with almost zero magnetic hysteresis are observed in these alloys. The effects of Mn/Co ratio on magnetic transition and magnetocaloric effects are discussed in this paper.

Low frequency acoustic properties of bilayer membrane acoustic metamaterial with magnetic oscillator

A bilayer membrane acoustic metamaterial was proposed to overcome the influence of the mass law on traditional acoustic materials and obtain a lightweight thin-layer structure that can effectively isolate low frequency noise. The finite element analysis（FEA） results agree well with the experimental results.It is proved that the sound transmission losses（STLs） of the proposed structures are higher than those of same surface density acoustic materials. The introduction of the magnetic mass block is different from the traditional design method, in which only a passive mass block is fixed on the membrane. The magnetic force will cause tension in the membrane, increase membrane prestress, and improve overall structural stiffness. The effects of the geometry size on the STLs are discussed in detail. The kind of method presented in this paper can provide a new means for engineering noise control.

TRANSIENT TEMPERATURE FIELD IN ACTIVE THRUST MAGNETIC BEARING

A transient temperature field model in a thrust magnetic bearing is built in which the heat resources come mainly from the eddy-current loss of solid cores and the copper loss of coils. The transient temperature field, system temperature rise and the thermo-equilibrium state during the rotor starting-up are calculated considering only the copper loss and the eddy-current loss. The numerical results indicate that the temperatures in coils and in magnets rise rapidly, their thermo-equilibrium states are formed within a short time. The temperatures in a thrust-disk and in a rotor rise slowly, their thermo-equilibrium states are formed aller a long period time. The temperatures of the thrust-disk and the rotor are far higher than the temperatures of coils and/or magnets aller the thermo-equilibrium state has come into being.

Behavior of Medium-frequency Core Loss in Fe-based Nanocrystalline Soft Magnetic Alloys

The dependences of the power loss per cycle on frequency have been investigated in the ranges of 100 Hz<= f<=25000 Hz and 0.1 T< =Bm <=1.0 T for three main original magnetic states in five sorts of Fe-based nanocrystalline soft magnetic alloys. The measured and calculated results showed that the total power loss per cycle clearly exhibited a nonlinear behavior in the range below 3 kHz～5 kHz depending on both the magnetic state and the value of Dm, whereas it showed a quasi-linear behavior above this range. The total loss was decomposed into hysteresis loss, classical eddy current loss and excess loss, the obvious nonlinear behavior has been confirmed to be completely determined by the dependence of the excess loss on frequency. It has been indicated that the change rate of the excess loss per cycle with respect to frequency sharp decreases with increasing frequency in the range below about 3 kHz～5 kHz, wherease the rate of change slowly varies above this range, thus leading to the quasilinear behavior of the total loss per cycle. In this paper, some linear expressions of the total loss per cycle has been given in a wider medium-frequency segment, which can be used for roughly estimating the total loss.

Effect of Cutting Techniques on the Structure and Magnetic Properties of a High-grade Non-oriented Electrical Steel

The high grade non-oriented electrical steel sheets containing 3.0%Si were manufacturing processed using different cutting techniques, then they were stress relief annealed（SRA）, the profiles and textures of the cutting edges were compared before and after annealing, and the magnetic properties of these specimens were tested and compared. The experimental results show that the iron loss of the specimen by water jet cutting is the lowest, but the magnetic induction under the low magnetic field is the highest, the iron loss of the specimen by laser cutting is the highest, but the magnetic induction under the low magnetic field is the lowest. It is necessary to adopt suitable production conditions and minimize the deterioration involved, and the magnetic property can be recovered by SRA effectively.

Comparative Study of Dielectric and Magnetic Properties of Selected 3D Reticulated Ceramics and Their Same Composition Ceramic Disks

3-dimensional reticulated ceramics (3DRCs) and their same composition ceramic disks(SCCDs) were fabricated by sol-gel method, with the composition of SrO-6Fe203(30%), SiC(35%) and Ti02(35%), sintered at 1200C in N2. The dielectric and magnetic parameters of such 3DRCs and their SCCDs were measured respectively in a temperature range from room temperature to 800癈 and in a frequency range from 2.6 GHz to 18 GHz. The results showed that the dielectric and magnetic loss of 3DRCs were obviously larger than those of their SCCDs in a wide range of temperature and the whole range of measuring frequency. The increase of dielectric loss of SDRCs was much higher than that of magnetic loss compared to their SCCDs, which was found due to the 3D net structure extrinsic characteristics.

Hysteresis loss reduction in self-bias FeSi/SrFe_(12)O_(19)soft magnetic composites

The magnetic field provided by magnetized SrFe_(12)O_(19)particles in FeSi/SrFe_(12)O_(19)composites is used to replace the applied transverse magnetic field,which successfully reduces the magnetic loss of the composites with minor reduction of permeability.This magnetic loss reduction mainly comes from the decrease in hysteresis loss,while the eddy current loss is basically unaffected.The hysteresis loss reduction in magnetized composites is believed to be due to the decrease in domain wall displacement caused by the increase in the average magnetic domain size in a DC magnetic field.This is an effective method for reducing the magnetic loss of soft magnetic composites with wide application potential,and there is no problem of increasing the cost and the volume of the magnetic cores.

Finite Element CAD Experiments on the Effect of Magnetic Loss in Power Transformers with Laminated Cores

The paper describes a simulated experiment that focuses on the numeric computation of magnetic loss in the laminated core of a single-phase power transformer. The students’ laboratory work is part of the library of experiments of the Electrical Machines virtual laboratory and makes use of the two-dimensional open-access electromagnetic field analysis software Finite Element Method Magnetics. The idea of the simulated exercise is to demonstrate how the magnetic loss caused by time-varying excitations affects the magnetic permeability, μ, of the laminated core and the terminal quantities of the energizing winding. A parametric analysis employing different values for the electrical conductivity and maximum hysteresis-induced angle of the laminated material yields five different field problems with increasing magnetic loss. Electric circuits characterized by the (I-V) operating point and reflected impedance of the energizing winding provide the information required to compute the changes in real power ΔP, reactive power ΔQ and magnetically stored energy ΔWm between successive problems characterized by increasing magnetic loss. The concept of reflected impedance helps to explain the physical meaning of the changes in power dissipation and energy storage in the laminated core.

In-situ grown Ni Co bimetal anchored on porous straw-derived biochar composites with boosted microwave absorption properties

With the gradually increasing protection awareness about electromagnetic pollution,the demand for absorbing materials with renewability and environmental friendliness has attracted widespread attention.In this work,composites consisting of straw-derived biochar combined with NiCo alloy were successfully fabricated through high-temperature carbonization and subsequent hydrothermal reaction.The electromagnetic parameters of the porous biocarbon/NiCo composites can be effectively modified by altering their NiCo content,and their improved absorbing performance can be attributed to the synergy effect of magnetic-dielectric characteristics.An exceptional reflection loss of-27.0 dB at 2.2 mm thickness and an effective absorption bandwidth of 4.4 GHz(11.7-16.1 GHz)were achieved.These results revealed that the porous biocarbon/NiCo composites could be used as a new generation absorbing material because of their low density,light weight,excellent conductivity,and strong absorption.

Self-assembly tungsten selenide hybrid ternary MOF derived magnetic alloys via multi-polarization to boost microwave absorption

Confronted with severe electromagnetic wave pollution,the development of high-performance electromagnetic wave shielding or absorbing materials is an effective way to deal with it.Notably,double transition metal alloys and transition metal dichalcogenides have attracted extensive attention in electromagnetic wave absorption,but few reports have studied the effects of these two materials on electromagnetic wave absorption at the same time.In this work,cobalt-based alloy with magnetic loss mechanism was selected for composition optimization.The ternary metal-organic framework was prepared by the one-step method,and then CoCu/C was prepared by high temperature annealing.Finally,in the hydrothermal process,ultra-thin tungsten selenide nanosheets were coated on the surface of magnetic component,and the final polyhedral WSe_(2)/CoCu/C composites with multiple heterogeneous interfaces were obtained.The synergistic effect of dielectric and magnetic components optimizes impedance matching and allows more electromagnetic waves to enter the absorber.Subsequently,through the conduction loss of high conductivity graphitized carbon,interfacial polarization,and dipole polarization of heterogeneous interfaces between the components,the magnetic loss provided by CoCu alloy can work together to maximize the attenuation ability of electromagnetic waves.Exactly,the minimum reflection loss(RLmin)value of the composite reaches-53.43 dB when the matched thickness is 2.1 mm,while the maximum effective absorption bandwidth(EABmax)reaches 6.0 GHz at a thin thickness of 1.8 mm.This work provides some support and reference for the design of novel electromagnetic wave absorbing materials via the dielectric/magnetic loss synergistic mechanism.

MOFs‑Derived Strategy and Ternary Alloys Regulation in Flower‑Like Magnetic‑Carbon Microspheres with Broadband Electromagnetic Wave Absorption

Broadband electromagnetic(EM)wave absorption materials play an important role in military stealth and health protection.Herein,metal–organic frameworks(MOFs)-derived magnetic-carbon CoNiM@C(M=Cu,Zn,Fe,Mn)microspheres are fabricated,which exhibit flower-like nano–microstructure with tunable EM response capacity.Based on the MOFs-derived CoNi@C microsphere,the adjacent third element is introduced into magnetic CoNi alloy to enhance EM wave absorption performance.In term of broadband absorption,the order of efficient absorption bandwidth(EAB)value is Mn>Fe=Zn>Cu in the CoNiM@C microspheres.Therefore,MOFs-derived flower-like CoNiMn@C microspheres hold outstanding broadband absorption and the EAB can reach up to 5.8 GHz(covering 12.2–18 GHz at 2.0 mm thickness).Besides,off-axis electron holography and computational simulations are applied to elucidate the inherent dielectric dissipation and magnetic loss.Rich heterointerfaces in CoNiMn@C promote the aggregation of the negative/positive charges at the contacting region,forming interfacial polarization.The graphitized carbon layer catalyzed by the magnetic CoNiMn core offered the electron mobility path,boosting the conductive loss.Equally importantly,magnetic coupling is observed in the CoNiMn@C to strengthen the magnetic responding behaviors.This study provides a new guide to build broadband EM absorption by regulating the ternary magnetic alloy.

A Flexible and Lightweight Biomass-Reinforced Microwave Absorber

Developing a flexible,light-weight and effective electromagnetic(EM)absorber remains challenging despite being on increasing demand as more wearable devices and portable electronics are commercialized.Herein,we report a flexible and lightweight hybrid paper by a facile vacuumfiltration-induced self-assembly process,in which cotton-derived carbon fibers serve as flexible skeletons,compactly surrounded by other microwave-attenuating components(reduced graphene oxide and Fe3O4@C nanowires).Owing to its unique architecture and synergy of the three components,the asprepared hybrid paper exhibits flexible and lightweight features as well as superb microwave absorption performance.Maximum absorption intensity with reflection loss as low as-63 dB can be achieved,and its broadest frequency absorption bandwidth of 5.8 GHz almost covers the entire Ku band.Such a hybrid paper is promising to cope with ever-increasing EM interference.The work also paves the way to develop low-cost and flexible EM wave absorber from biomass through a facile method.

Macroscopic electromagnetic synergy network-enhanced N-doped Ni/C gigahertz microwave absorber with regulable microtopography

To achieve excellent electromagnetic wave(EMW)absorption properties,the microstructure design of the absorber is critical.In this work,six kinds of N-Ni/C nanostructures with different morphologies were prepared by one-step hydrothermal method and high temperature carbonization by adjusting the types of nickel salts and reaction solvents.The EMW absorption performance of six different morphologies of N-Ni/C nanostructures was compared and analyzed.Among them,it is found that the nanoflowerlike N-Ni/C composite has excellent dielectric loss and magnetic loss synergistic effect due to its polycrystalline structure,and can obtain excellent EMW absorption performance.The minimum reflection loss value at a thickness of 1.9 mm is-59.56 dB at 16.88 GHz,and the effective absorption bandwidth value reaches 6.0 GHz at a thickness of 2.2 mm.Our research shows that different morphologies and multiple lattice structures of nanostructures with the same composition have a significant influence on EMW absorption performance,which provides new research ideas for developing high-performance EMW absorbing materials.

Lightweight,self-cleaning and refractory FeCo@MoS_(2)PVA aerogels:from electromagnetic wave-assisted synthesis to flexible electromagnetic wave absorption

The emergence of wearable and foldable electronic devices urges advanced electromagnetic(EM)wave absorbers with maintained performance under deformation.Here FeCo@MoS_(2)poly vinyl alcohol(PVA)aerogels have been fabricated with the assistance of EM waves for simultaneous splitting of the MoS_(2)flakes and dispersive growth of FeCo nanoparticles.The resultants in-return have been used for EM wave absorption with excellent performance,providing minimum reflection loss(RL_(min))of-40.7 dB and a broad effective absorption bandwidth(EAB)of 6.4 GHz at a thickness of 2.5 mm.Real-time compression has been introduced to reveal the evolution of EM parameters.The aerogels maintain satisfactory performance even under 50%compression due to the balance of impedance matching and attenuation.Despite the deterioration of impedance matching,the attenuation is significantly enhanced due to both strengthened conductive loss and magnetic loss.In addition,features such as lightweight,self-cleaning and refractory can be achieved for the aerogels for applications in complex environments.As such this work not only provides a versatile synthetic route assisted by EM wave energy,but also insights on the evolution of absorption performance under deformation together with the design strategy of multifunctional flexible wave absorbers.

Microwave-Absorbing Properties of La_(1-x)Sr_xMn_ (1-y)Fe_yO_3

The experiment samples of La1-xSrxMn1-y FeyO3（x = 0. 15, 0.20, 0.23; y = 0. 10, 0. 12, 0.14, 0.16） were prepared by sol-gel process, and the loss tangent and absorption coefficient in the range of 2 - 18 GHz were measured by HP8722 net analyzing apparatus. It is found that changing the content of Sr or Fe would effect the microwave absorbing. When the thickness of La1-x SrxMn1-y FeyO3 is 2 mm and x =0.20, y = 0.14, the capability of microwave absorbing is the best one. There are two absorption peaks; the maximum is 34 dB and effective band width with 10 dB and more reaches 6.2 GHz.

A finite oxidation strategy for customizing heterogeneous interfaces to enhance magnetic loss ability and microwave absorption of Fe-cored carbon microcapsules

Metallic iron particles are of great potential for microwave absorption materials due to their strong magnetic loss ability.However,the oxidation susceptibility of metallic iron particles in the atmospheric environment is regarded as a major factor causing performance degradation.Although many efforts have been developed to avoid their oxidation,whether partial surface oxidized iron particles can improve the microwave absorbing performance is rarely concerned.In order to explore the effect of partial surface oxidation of iron on its properties,the designed yolk–shelled(Fe/FeO_(x))@C composites with multiple heterointerfaces were synthesized via an in-situ polymerization and a finite reduction–oxidation process of Fe_(2)O_(3)ellipsoids.The performance enhancement mechanisms of Fe/FeO_(x)heterointerfaces were also elaborated.It is demonstrated that the introduction of Fe-based heterogeneous interfaces can not only enhance the dielectric loss,but also increase the imaginary part of the permeability in the higher frequency range to strengthen the magnetic loss ability.Meanwhile,the yolk–shell structure can effectively improve impedance matching and enhance microwave absorption performances via increasing multiple reflection and scattering behaviors of incident microwaves.Compared to Fe@C composite,the effective absorption(reflection loss(RL)<−10 dB)bandwidth of the optimized(Fe/FeO_(x))@C-2 increases from 5.7 to 7.3 GHz(10.7–18.0 GHz)at a same matching thickness of 2 mm,which can completely cover Ku-band.This work offers a good perspective for the enhancement of magnetic loss ability and microwave absorption performance of Fe-based microwave absorption materials with promising practical applications.