Experimental research based on a C-band compact transit-time oscillator with a novel diode loading an embedded soft magnetic material and shielding structure

In order to reduce the external magnetic field and improve the conversion efficiency of high-power microwave generation devices with low external magnetic field,a novel diode with an embedded soft magnetic and shielding structure is proposed.The soft magnetic material is designed to enhance the local magnetic field in the diode region.Moreover,the diode applies a shielding structure which can reduce the radial electric field.From simulation research,it is found that the emission and transmission quality of the electron beam with low magnetic field is greatly improved when loading this diode.Through simulation research,it is verified that the diode can increase the conversion efficiency of the transit-time oscillator(TTO)from 30%to 36.7%.In our experimental study,under the conditions of a diode voltage of 540 kV and a current of 10.5 kA,the output microwave power is 1.51 GW when loading the novel diode and the microwave frequency is 4.27 GHz when an external guiding magnetic field of 0.3 T is applied.The corresponding conversion efficiency is improved from 20.0%to 26.6%,which is 6.6%higher than that of a device loaded with a conventional diode.Our experiments have verified that this novel diode can effectively improve the conversion efficiency of high-power microwave sources operating with low magnetic field,and contribute to the miniaturization and compactness of high-power microwave devices.

Hopkinson Effect in Soft Magnetic Materials

The μi-T curves of the alloy Fe73.5Cu1 Nb3Si13.5B9 in the amorphous state and in the nanocrys-talline state have been investigated. For comparison, μi-T curves of the other two kinds of typical soft magnetic alloys also have been measured. It was found that a sharp Hopkinson peak appeared at the Curie point for each amorphous and crystalline alloy but there was no Hopkinson peak for the nanocrystalline alloy at the Curie point of the residual amorphous phase. This phenomenon has been explained in terms of the characteristic temperature dependence of the effective magnetic anisotropy.

High permeability and bimodal resonance structure of flaky soft magnetic composite materials

We establish a theoretical bimodal model for the complex permeability of flaky soft magnetic composite materials to explain the variability of their initial permeability.The new model is motivated by finding the two natural resonance peaks to be inconsistent with the combination of the domain wall resonance and the natural resonance.In the derivation of the model,two relationships are explored:the first one is the relationship between the number of magnetic domains and the permeability,and the second one is the relationship between the natural resonance and the domain wall resonance.This reveals that the ball milling causes the number of magnetic domains to increase and the maximum initial permeability to exist after 10 h of ball milling.An experiment is conducted to demonstrate the reliability of the proposed model.The experimental results are in good agreement with the theoretical calculations.This new model is of great significance for studying the mechanism and applications of the resonance loss for soft magnetic composite materials in high frequency fields.

Development of Rapidly Quenched Soft Magnetic Materials in China

The discovery of the first Fe-based ferromagnetic amorphous alloy in 1966 had made an impact on conventional magnetic materials because of its unique properties. Since then, a number of amorphous magnetic materials have been successfully developed and used in a wide variety of applications. A brief review of R & D activities on amorphous soft magnetic materials in China is given from the beginning to the present in a somewhat chronological order, followed by a brief introduction to their applications on electric and electronic industries. An analysis and a prospect of Chinese market of such amorphous materials are also presented.

Techniques and Apparatus for Measuring Rotational Core Losses of Soft Magnetic Materials

In many situations such as the cores of a rotating electrical machine and the T joints of a multiphase transformer, the local flux density varies with time in terms of both magnitude and direction, i.e. the flux density vector is rotating. Therefore, the magnetic properties of the core materials under the rotating flux density vector excitation should be properly measured, modeled and applied in the design and analysis of these electromagnetic devices. This paper presents an extensive review on the development of techniques and apparatus for measuring the rotational core losses of soft magnetic materials based on the experiences of various researchers in the last hundred years.

Excellent soft magnetic properties realized in FeCoN thin films

FeCoN soft magnetic thin films are prepared by using the reactive direct-current magnetron sputtering technique. It is found that the addition of N2 can reduce the coercivity of the FeCoN film, and excellent soft magnetic properties can be obtained when the ratio of N2 flow to total gas flow is 10%. The influences of texture, grain size, and stress on the magnetic properties and the high-frequency behaviors of the films are also discussed.

Serrated magnetic properties in metallic glass by thermal cycle

Fe-based metallic glasses（MGs） with excellent soft magnetic properties are applicable in a wide range of electronic industry. We show that the cryogenic thermal cycle has a sensitive effect on soft magnetic properties of Fe78Si9B13 glassy ribbon. The values of magnetic induction（or magnetic flux density） B and Hc coercivity c show fluctuation with increasing number of thermal cycles. This phenomenon is explained as thermal-cycle-induced stochastically structural aging or rejuvenation which randomly fluctuates magnetic anisotropy and, consequently, the magnetic induction and coercivity. Overall,increasing the number of thermal cycles improves the soft magnetic properties of the ribbon. The results could help understand the relationship between relaxation and magnetic property, and the thermal cycle could provide an effective approach to improving performances of metallic glasses in industry.

Mossbauer Spectroscopy of Fe-Ni-Nb-B Alloy in Weak Magnetic Field

Amorphous and nanocrystalline (Fe1–xNix)81Nb7B12 (x = 0, 0.25, 0.5, 0.75) alloys were measured by M?ssbauer spectrometry in the weak external magnetic field of 0.5 T. From structural analyses, ferromagnetic bcc-FeNi and fcc-FeNi and paramagnetic (Fe-Ni)23B6 phases were identified in the annealed samples. It was shown that in the external magnetic field the intensities of the 2nd and the 5th lines (A23 parameter) are the most sensitive M?ssbauer parameters. Rather small changes were observed in the values of internal magnetic field. Our results showed that the amorphous precursor is more sensitive to the influence of external magnetic field than the nanocrystalline alloy. All spectra of amorphous precursor showed the increase of A23 parameter and decrease of internal magnetic field values of about 1 T (±0.5 T) under influence of external magnetic field. In the case of nanocrystalline samples the tendency for the values of internal magnetic field is similar but the effect is not so pronounced. The measurements confirmed that even weak external magnetic field affected orientation of the net magnetic moments. Our results indicate that effect of the external magnetic field is stronger in the case of amorphous samples due to their disordered structure.

Design and Performance Analysis of Permanent Magnet Claw Pole Machine with Hybrid Cores

Permanent magnet claw pole machine(PMCPM) is a special kind of transverse flux permanent magnet machine. Compared with other electrical machines, it has the advantages of high torque density and high efficiency for high speed operation. However, because of its complex irregular structure, the manufacturing process using silicon sheets is complicated. Soft magnetic composite material(SMC) is manufactured by powder metallurgy technology, which can produce various shapes of stator core structures, so it is easier to produce various irregular shapes of the stator core. However, the raw SMC material is relatively expensive, and the mechanical strength of SMC is weak. In this paper, a PMCPM with hybrid cores is proposed. With the adoption of hybrid silicon sheet-SMC cores and amorphous alloy-SMC cores, the torque ability of PMCPM can be improved greatly and it can have higher efficiency for more wide operation frequency. Meanwhile, its mechanical strength has been improved and it can be designed for high torque direct drive applications as it is a modular machine. Furthermore, three methods are proposed to reduce the additional eddy current loss which resulted from the employment of hybrid cores in PMCPM.

A multi-parameter model of heat treatment process for soft magnetic materials on performance of HSERs

Abstract:Material properties play an important role in the performance of electromagnetic mechanism. For an aeronautic Hermetically-Sealed Electromagnetic Relay(HSER), more than 50%parts are made of soft magnetic materials. Therefore, the performance of soft magnetic materials directly determines the static and dynamic characteristics of the HSER. Based on the theory of crystal recrystallization, this paper analyzes cold extrusion and heat treatment in the processing of soft magnetic materials, simulates the grain change process of an armature at different heat treatment temperatures, establishes a correlation model of temperature, grain size, and magnetic energy,and verifies results by scanning electron microscopy. Results of heat treatment temperatures from 800 ℃to 920 ℃are obtained and compared. A sample soft magnetic material after heat treatment at different temperatures has the largest difference in the initial magnetization range, up to 22%. In order to verify the fluctuation of the overall output characteristics of an HSER caused by the difference between soft magnetic materials, a static and dynamic analysis model of a typical HSER is established, and the accuracy of the model is verified by a set of actual test system. The difference of dynamic characteristics under different heat treatment temperatures is nearly 3%.

Electromagnetic Characteristics and Corrosion Resistance of New Magnetosoft Materials Based on Capsulated Iron Powders

A new method of depositing an insulating multifunctional oxide coating on metal particles was developed.Such coatings increase corrosion resistance and insulate metal particles from each other.On base of capsulated by oxide coating water-atomized iron powder ASC100.29,new composite soft magnetic materials were synthesized,which are able of replacing electrical steel in devices.Structural,electromagnetic properties and corrosion characte-ristics of the obtained composites were studied.It was found that the synthesized composite materials have low elec-tromagnetic losses,high values of magnetic induction(up to 2.1 T)and good corrosion resistance.The results demon-strate that the use of such materials in power supplies,c hokes,transformers,stators and rotors of electric machines and other products ensures their stable operation under various conditions.

Analysis and Application of the Series Core Snubber

The transformer core snubber （CS）, as one of the most important components in the EAST （experimental advanced superconducting tokamak） NBI （neutral beam injector） system, is designed to limit grid damage and protect the ion source during periods of electrical breakdowns. A transformer core snubber is analyzed in detail in this paper. Several kinds of soft magnetic cores are presented and compared. With analysis and experiment on the basic characteristics of the cores, the most suitable materials are suggested. The circuit simulation code is established which could simulate faulty conditions with concentrated and distributed CS concepts. Based on the above work, an ion source CS is developed with series type of distributed topology. The CS has been subjected to experimental validation at 80 kV with a peak short-current of approximately 400 A in a real NBI system, which proves the accuracy of the adopted assumptions and the analysis method.

Study on the influence of armature on the efficiency of reluctance accelerator

The armature is an important part affecting the energy conversion efficiency of a reluctance accelerator.In this paper,six kinds of soft magnetic materials are chosen and four structures are designed for the armature.At first,the circuit and magnetic force are theoretically analyzed.Then the armatures with different materials and structures are used in the simulation,and the performances are compared and analyzed.At last,the experiment verifies the theory analysis and simulation design.It is concluded that the saturation flux density and conductivity of the material are the key factors affecting the armature force,and the optimization of armature structure can effectively restrain the eddy current,reduce negative force and improve efficiency.Compared with cutting slits in solid armatures,laminating the sheets radially can reduce the eddy current more efficiently.Although slitting can prevent the eddy current to a certain extent,meanwhile,it will decrease the magnetic force because of the losing of magnetized volume and the surface area.Hence,choosing the high saturation flux density material and making out the armature with radially_laminated sheets will improve the efficiency of the reluctance accelerator.In this paper,the silicon steel radially_laminated armature is a better choice for the armature design of the reluctance accelerator.

Microstructure and Magnetic Properties of Fe-Ni Alloy Fabricated by Selective Laser Melting Fe/Ni Mixed Powders

Fe-Ni alloy, as a widely applied ferromagnetic material, is synthesized using selective laser melting （SLM）. The chemical compositions and microstructure of the SLM Fe-Ni alloy are characterized by X-ray diffraction （XRD）, energy dispersive X-ray spectroscopy and scanning electron microscopy. It was found that the samples exhibited fine grains with homogenous distribution when a low laser scanning velocity was used. Moreover, the magnetic properties of the samples with different laser parameters are also measured. It shows that the SLM Fe-30%Ni alloy possesses a low coercivity and high saturation magnetization. It also can be obtained that SLM is an alternative faster method to prepare soft magnetic material with complex shapes. Moreover, the magnetic properties can be influenced by the laser parameters.

Microstructure change in Fe-based metallic glass and nanocrystalline alloy induced by liquid nitrogen treatment

The effects of acyclic liquid nitrogen(LN)treatment in a temperature range of-196℃to 50℃on the thermal and magnetic stability of Fe78Si9B13 and Fe73.5Si13.5B9Nb3Cu1 glassy ribbons have been studied.The intrinsic heterogeneities of the metallic glasses can be activated through cryogenic thermal cycling,making irreversible structural changes after the treatment and inducing rejuvenation to the materials.The microstructural changes of both Fe-based metallic glass(MG)and nanocrystalline alloy induced by LN treatment were investigated.The experimental results show that the LN treatment could effectively rejuvenate the Fe-Si-B MGs and change their thermomechanical and magnetic properties.Based on the partially-crystallinity and well-known magnetic constants,the increase of the energy at the order of 10m J/g and magnetic domain wall movement and rotation at the order of 5-6μm and 0.5°-0.8°are found for FINEMET-type amorphous alloy after LN treatment.It is also found that LN treatment can contribute a little stored energy to the magnetic domain wall movement and magnetic domain rotation.

Thermodynamics and Magnetostriction of Fe-Co-B-Si-Nb-C Bulk Metallic Glasses

Fe-Co-B-Si-Nb-C glassy alloy with the addition of C was prepared by arc melting and copper suck-casting. The thermodynamics and soft magnetic properties were investigated. The casted amorphous alloys were heat-treated at different temperatures. The differential scanning calorimeter （DSC） results and thermal expansion show complete thermodynamics of crystallization. Its magnetostriction properties were studied by capacitance method. Saturation magnetostriction increases to 38×10^-6. The amorphous alloy exhibits good soft magnetic properties with low coercivity and high saturation magnetic induction. The results show that minor addition of C is beneficial to enhance the saturation magnetostriction λs, and do not deteriorate the ability of forming amorphous.