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Spinning Rotor Gauge is widely used in the field of metrology as a deputy standard vacuum gauge. The lower measurement limit of this vacuum gauge depends on other influencing factors in addition to background gas molecular friction damping. The damping caused by these factors is collectively called residual damping. this paper analyzes the impact of damping caused by eddy currents in residual damping, quantitatively describes the electromagnetic torque and eddy current heating power generated by eddy currents in the interior and surface of the rotor, calculates the corresponding kinetic energy loss, and obtains the simulated value of rotor attenuation. The attenuation calculated through simulation within 12 h is 0.23Hz, corresponding to an average background pressure of 7×10-5Pa. Compare this with the actual observed residual damping result of an attenuation of 1.17Hz and a background of 1.6308×10-4Pa. A high consistency is obtained, which proves the reliability of the numerical model establishment method and calculation results of residual damping caused by eddy current introduced in this article. [Display omitted] • Conducted dynamic modeling and computer simulation to capture rotor dynamics accurately under real experimental conditions. • Explored unique eddy current formation mechanisms on the 4.5 mm diameter spherical rotor, distinct from similar systems. • Quantitatively calculated energy loss due to eddy currents, integrating it into an iterative computer program to generate rotation speed attenuation curves. • Demonstrated consistent results between simulated and observed rotor rotation attenuation curves. • Pioneered quantitative assessment of eddy currents' impact on background in the Spinning Rotor Gauge, yielding precise results. The Spinning Rotor Gauge (SRG) serves as a crucial tool in metrology as a secondary standard vacuum gauge. However, its lower measurement limit is not solely determined by background gas molecular friction damping but is also affected by other contributing factors, collectively termed residual damping. This paper investigates the influence of eddy currents on residual damping. It quantitatively analyzes the electromagnetic torque and eddy current heating power induced within the rotor's interior and surface, calculates the corresponding kinetic energy loss, and simulates the rotor's attenuation. The simulation predicts an attenuation of 0.23 Hz within a 12-hour period, corresponding to an average background pressure of 7 × 10-5 Pa. A comparison with observed residual damping data, showing an attenuation of 1.17 Hz and a background pressure of 1.6308 × 10-4 Pa, demonstrates high consistency. This affirms the reliability of the numerical model and calculation results regarding eddy current-induced residual damping presented in this article. [ABSTRACT FROM AUTHOR]

Transition metal carbides/carbonitrides (MXene) exhibit huge potential as electromagnetic wave (EMW) absorbers in dealing with electromagnetic radiation problem that rise due to the rapid development of 5G era. The incorporation of magnetic materials can effectively mitigate the impedance mismatch and singular loss mechanisms inherent in pure MXenes (PMs). However, challenges persist due to issues such as random distribution, complex preparation processes, and inadequate interaction. In this study, Ti 3 C 2 T x /Ni hybrids were synthesized using a one-pot method, wherein Ni, derived from molten salt, replaces Al layer of MXene, facilitating the in-situ growth of Ni nanocomponents within the interlayered region. The periodic electromagnetic synergetic network of "MXene-Ni-MXene-Ni-MXene" provides substantial magnetic resonance, eddy current loss, interface polarization, defect polarization, and dipole polarization, enriching the loss mechanism. By regulating the concentration of Ni, the intrinsic poor impedance matching of MXene was improved. Consequently, Ti 3 C 2 T x /Ni hybrid exhibited exceptional electromagnetic wave absorption (EMA) performance, achieving a reflection loss (RL) of −64.51 dB and an effective absorption bandwidth (EAB) of 4.96 GHz at a matching thickness of 1.98 mm. Additionally, the super radar cross-section (RCS value = −15.73 dB m2) endow it potential in practical application. This work provides a facile method for achieving unique electromagnetic synergetic loss mechanism, thus paving the way for exploring high-efficient MXene-based EMW absorbers. [Display omitted] [ABSTRACT FROM AUTHOR]

Achieving low-frequency broadband electromagnetic wave absorption in extreme environments over 2000 °C is challenging. Biomimetic hierarchy materials of high entropy lanthanide carbides were designed to optimize electromagnetic wave absorption. Composite microspheres of (Hf 0.2 Zr 0.2 Ti 0.2 Ce 0.2 La 0.2)C 1-δ and SiC embedded in pyrolytic carbon (MC/PyC) were prepared by using the electro-spray method followed by heat treatment. The specimens of MC/PyC microspheres with a thickness of 2.5 mm exhibited a minimum reflection loss value of − 48.9 dB, and electromagnetic wave absorption from 4.0 GHz to 17 GHz. The enhanced absorption capability is attributed to the synergistic effect of dielectric losses from conduction and polarization, along with magnetic losses due to eddy currents and natural resonance of the high-entropy carbides within the multiscale pores. The composition and featured microstructure MC/PyC microspheres were noteworthily stable under the 2200 °C oxyacetylene ablation, ensuring consistent high-performance electromagnetic wave absorption even in harsh conditions. [ABSTRACT FROM AUTHOR]

Owing to their low resistivity, metal-based magnetostrictive materials are prone to eddy current loss under high-frequency magnetic field excitation, leading to a significant decline in output characteristics. Cobalt ferrite, a new non-metal-based magnetostrictive material, possesses both high magnetostriction strain and high resistivity, making it highly promising for high-frequency driving applications. However, reports on cobalt ferrite as the core driving material for ultrasonic transducers remain limited, and research on its high-frequency vibration characteristics is insufficient. In this study, magnetostrictive samples of cobalt ferrite were prepared using a solid-state reaction method, and their morphologies and magnetic properties were characterized. Under a bias magnetic field, the dynamic magnetic properties of cobalt ferrite and temperature variations with the driving magnetic field amplitude and prestress were analyzed. The results indicated that the density of the sample prepared by solid-state reaction can reach 88 % and the saturation magnetostriction coefficient λ s can reach 186 × 10−6, with an optimal bias range of 400–600 Oe for the cobalt ferrite. When the driving magnetic field amplitude is 100 Oe in the optimal bias range, the output amplitude of the cobalt ferrite is 2160 nm, meeting the output requirement of high-frequency magnetostrictive ultrasonic transducers. • Cobalt ferrite magnetostrictive material for high frequency ultrasonic transducers was prepared based on solid state reaction. • Testing the magnetostrictive properties of cobalt ferrite using the static and dynamic magnetic properties test platforms. • The static magnetostrictivity of cobalt ferrite decreases with the decrease of density and the increase of prestress. • The dynamic magnetostrictive properties under a bias magnetic field with driving magnetic field and pre-stress was discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe/C composites were successfully synthesized using a hydrothermal method. • The Fe/C composite has a bandwidth of 12-18 GHz at a thickness of 1.70 mm, covering the entire Ku band. • Mangosteen shells are widely available, economical and environmentally friendly, and highly utilizable. It is well known that magnetic iron oxide (Fe 3 O 4) and carbon-based materials are good microwave absorbing materials. However, the frequency bands in which Fe 3 O 4 absorbs electromagnetic waves are usually concentrated in the low-frequency region, whereas carbon materials are in the high-frequency region. Therefore, this study aims to deal with the limitation of the absorption bands of these two substances. In this work, this Fe 3 O 4 /C composite with high performance microwave absorption was successfully adoption of hydrothermal-calcination process using mangosteen shells as a biomass carbon material, and with a thickness of 1.97 mm, the optimal reflection loss of the sample can reach −67.49 dB, and the frequency band that can be absorbed is 4.32 GHz. The interface polarization, dipolar polarization and eddy current loss in Fe 3 O 4 and carbon materials produce synergistic effects, and the porous conductive network increases the electromagnetic wave transmission path and generates conductive losses, which results in composites with excellent electromagnetic wave absorption properties. The findings indicated that a composite compound of Fe 3 O 4 and carbon-based material was successfully synthesized by hydrothermal method and obtained a materials with outstanding electromagnetic wave absorption properties and high absorption bandwidth. [ABSTRACT FROM AUTHOR]

Ni 0.2 Mn 0.4 Zn 0.4 Fe 2 O 4 (NMZF) nanoparticles were anchored on the surface of MXene(Ti 3 C 2 T x) to form Ti 3 C 2 T x /NMZF nanocomposites for optimization of microwave absorption performance. The Ti 3 C 2 T x /NMZF nanocomposites were synthesized by using a four-step strategy, including sonication, stirring, hydrothermal reduction and vacuum drying. More than 40 percent of the NMZF nanoparticles in this nanocomposite were assembled to form a conductive network. Meanwhile, the multilayer MXene acted as a framework to host the NMZF nanoparticles, providing dipolar polarization, interfacial polarization and eddy current loss. Benefiting from the structure design of MXene, combined with magnetic materials and optimized impedance matching, the Ti 3 C 2 T x /NMZF exhibited a minimum reflection loss (RL min) of −57.39 dB, with a thickness of 2.97 mm and an effective absorption bandwidth (EAB) of 3.2 GHz. Therefore, such a facile method could be used to construct nanocomposites with microwave absorption performance (-57.39 dB, 3.2 GHz), so as to address microwave pollution issues. • The EMA performance of MXene/NMZF composites can be controlled through regulating ratio of MXene and NMZF nanoparticles. • The optimal reflection loss of the MXene/NMZF composite is −57.39 dB, and the bandwidth is up to 3.2 GHz. • The excellent MA properties originated from synergy effect, more polarization loss and multiple reflections. • The negative effect of magnetic materials on microwave absorption can be solved by adding the non-magnetic elements. [ABSTRACT FROM AUTHOR]

This paper introduces a novel design for a soft magnetic core (SMC) using laminated nanocrystalline flake ribbons (NFR) to improve the efficiency and thermal performance of EV wireless charging. The nanocrystalline ribbons, with configurable permeability, offer high flexibility, high power density, and low core loss for the vehicle assembly (VA) side in inductive power transfer (IPT) applications. However, the lamination structure and high conductivity of the material present challenges in analyzing loss characteristics. This paper systematically addresses these issues. Firstly, NFR materials with varying permeabilities are analyzed using traditional toroidal measurements. Next, the flux distribution and eddy current losses due to norm flux in IPT are considered. Finite element method (FEM) simulations are then utilized to illustrate the impact of additional eddy current losses and the imbalance caused by the lamination structure. A multi-segment, multi-permeability core structure is proposed to optimize core loss, coupling coefficient, and flux density distributions. Finally, experiments are conducted to assess the new design's performance. The proposed structure achieves a DC-DC efficiency of 95.68% at 12.78 kW output power and maintains optimized efficiency even with aluminum shielding. Additionally, improvements in temperature distribution uniformity and thermal stability are observed, demonstrating superior performance compared to traditional ferrites. • Soft magnetic cores affect efficiency & thermal performance in EV wireless charging • Loss analysis conducted for permeability-configurable NFR cores in IPT applications • FEM reveals the loss features and imbalances in flux and loss distributions • Optimization process considers the core loss, coupling, and thermal distributions • The multi-segment multi-permeability core improves the overall system performance [ABSTRACT FROM AUTHOR]

In [[1]], to address the problems of excessive tension, speed and fluctuation in long-distance traditional single high-power motor centralized drive belt conveyors, a distributed permanent magnet direct-drive belt conveyor system is designed. Conclusions and Future Works This Special Issue includes four papers focusing on multi-factor coupling analysis and optimization methods for high-quality electrical machine systems to further improve performances so as to maintain customized demands in the field of new energy resources. High-quality electrical machine systems used as energy conversion equipment to generate and utilize electric energy have become indispensable and attracted increasing attention in advanced industrial production and transportation electrification. [Extracted from the article]

[Display omitted] • ZIF-67 derived CoNi@carbon/RGO with heterogeneous interfaces were synthesized by a facile method for EMW absorption. • The RL min of CoNi@carbon/RGO-15 reaches -41.09 dB, EAB can reach 5.41 GHz with a thickness of 1.5 mm. • The RGO, Co/C, and Ni nanoparticles constructed a 3D structure that has high conduction loss and eddy current loss. The controllable structure design and composition regulation play a key role in the development of electromagnetic wave (EMW) absorbing material. Herein, CoNi@carbon/RGO absorbing materials were successfully prepared by direct pyrolysis of ZIF-67/Ni(OH) 2 /GO precursor. The CoNi@carbon/RGO-15 sample achieves an RL min value of −46.14 dB and an effective absorption bandwidth (EAB) of 1.15 GHz (thickness 4.1 mm) at a low frequency with a filling amount of only 10 wt%. When the thickness is 1.5 mm, the RL min reaches −41.09 dB and the EAB reaches 5.41 GHz, covering most of the Ku bands. After the pyrolysis, the carbon layer, Co and Ni nanoparticles, and RGO nanosheets form a three-dimensional porous structure, which builds up abundant heterogeneous interfaces and conductive networks. These factors can enhance impedance matching, dielectric, and magnetic loss. This indicates that CoNi@carbon/RGO is the potential lightweight EMW absorbing material with high performance. [ABSTRACT FROM AUTHOR]

This study proposes an improved multi-frequency eddy current array sensor for the accurate detection of micro-defects (under-welding, over-welding, partial welding breakage, and minute penetration holes) of welding seam in metal plates. The primary goal is to further reduce the external and internal noise of the induced coil by optimizing the composition structure of the eddy current probe, thereby improving its sensitivity and signal-to-noise ratio in micro-defect detection. In response to the issue of external noise, this research introduces a gradient differential coil model, which can compensate for initial errors based on a geometrically balanced structure. By establishing a 3D simulation model and a physical mechanical structure, the suppression effect of this structure on excitation magnetic field and external environmental interference is verified. Furthermore, for the internal noise, a mathematical model of the direct stranded litz wire is established. Theoretical calculations and experimental validation confirm that the litz wire exhibits lower eddy current loss and higher Q value compared to traditional copper conductors, thus mitigating internal noise and improving signal-to-noise ratio. On this basis, the excitation mode of the eddy current coil probe array is set to a multi-frequency excitation method based on a center frequency, greatly reducing the electromagnetic interference between channels. Experimental results demonstrate that the improved eddy current sensor can effectively recognize as low as Φ1 mm weld penetration defect at a lift-off value of 0.5 mm, achieving a remarkably high signal-to-noise ratio of approximately 17.7 dB. [Display omitted] • The gradient differential coil structure effectively attenuates environmental noise. • High-frequency Litz wires minimize eddy current losses, consequently enhancing the signal-to-noise ratio. • The multi-frequency excitation method effectively eliminates crosstalk between adjacent coils. • This design achieves a remarkable combination of high sensitivity and rapid detection capabilities. [ABSTRACT FROM AUTHOR]

The Fe-based nanocrystalline has been widely used in the innermost magnetic shielding of the spin-exchange relaxation-free (SERF) magnetometer due to its high permeability and low magnetic noise, which are significant factors limiting the sensitivity and accuracy of the measurements. However, the operating temperature of the inner shielding layer is around 80°C, and temperature has a significant impact on the magnetic noise of Fe-based nanocrystalline. To precisely analyze the magnetic noise of the Fe-based nanocrystalline in the SERF magnetometer, we first numerically simulate the 1K107 Fe-based nanocrystalline magnetic shielding barrel using the finite element method (FEM). Then, a variable-temperature dynamic Jiles-Atherton (VTDJA) model is proposed. The losses of 1K107 under various temperature are separated. The magnetic noise of 1K107 is computed using the Fluctuation-Dissipation theory. Finally, the magnetic noises of 1K107 at 25℃ and 80℃ are measured by setting up an experimental test system. Results show that the simulated deviation of the magnetic noise at 80°C and 25°C is 32 %, and the actual measured deviation is 48 %. The errors between simulated and measured magnetic noises at 25°C and 80°C are 5.29 % and 6.54 %, respectively. This study provides a novel method for the performance optimization of the SERF magnetometer. [Display omitted] • A novel method for calculating magnetic noise of Fe-based nanocrystalline based on temperature variation is proposed. • A novel variable-temperature dynamic J-A hysteresis model is proposed to separate the loss of Fe-based nanocrystalline. • The eddy current loss noise is the main magnetic noise of Fe-based nanocrystalline at 25℃-90℃ and 20–100 Hz. • The errors between simulated and measured noises at 25 °C and 80 °C are 5.29 % and 6.54 %, respectively. [ABSTRACT FROM AUTHOR]

• Developing a comprehensive model of a transformer winding which incorporates skin effect, proximity effect, and eddy current losses in the core, • Studying the effects of the core at high frequencies using simulations and measurements, • Investigating the skin and proximity effects on the frequency response and impedance characteristics of transformers, • Performing empirical measurements to validate the reduced influence of the core at high frequencies. This paper investigates the high-frequency transformer losses attributed to eddy currents in both conductors and the core. A comprehensive model of a transformer winding is presented, meticulously incorporating skin and proximity effects. The winding resistance increase due to these effects is determined by applying analytical and finite element methods. The investigation highlights that eddy current losses in the magnetic core notably increase the resistance of each winding section in low frequencies. However, the impact of these losses diminishes as the winding length approaches the voltage wavelength at high frequencies. Consequently, the net magnetomotive force and flux in the core become negligible. As a result, the high-frequency impedance characteristics are remarkably similar for windings with and without a magnetic core. These findings are substantiated through rigorous simulations and empirical measurements. [ABSTRACT FROM AUTHOR]

• Broadband and multimodal iron loss analyses were performed for Mn-Zn ferrite, Finemet wound, and Sendust powder cores. • These cores exhibit universal features on iron loss against frequency. • Iron loss analyses based on magnetization process well corresponds to the Bertotti's statistic model. Since iron loss of soft magnetic devices has been one of the major energy loss components in a modern power electronics system, it is crucially important to understand the physical mechanisms of iron loss. For this issue, the classical Steinmetz equation-based analysis has been widely utilized for the iron loss decomposition into hysteresis loss, classical eddy current loss, and excess loss. In this study, multimodal iron loss analyses based on magnetization processes were adopted for Mn-Zn ferrite sintered core, FINEMET wound core, and previously reported Sendust powder core [N. Ono et al., IEEE Trans. Magn. 59 , 6301305 (2023)], which have quite different magnetic and electronic properties. These analyses revealed that all the cores studied in this work commonly exhibited to change the magnetization process from irreversible to reversible with increasing the frequency, which correspond to magnetic domain wall displacement and magnetization rotation, respectively. The transition frequency of the magnetization process significantly depends on the samples. The classical Steinmetz based analysis and the statistic model which is the theory to explain the excess loss were compared with the above iron loss analyses. Consequently, the iron loss components of irreversible and reversible magnetization processes are well consistent with the sum of hysteresis and excess losses and the classical eddy current loss, respectively. Moreover, the magnetic object introduced as a conceptual parameter of the statistic model corresponds to the effective domain wall number. [ABSTRACT FROM AUTHOR]

FeSiAl soft magnetic composites (SMCs) with phosphate-silicone resin as the insulating layer were prepared by phosphating FeSiAl powder with K 3 PO 4 solution. The effects of K 3 PO 4 content on the microstructure and composition of the insulation coating were investigated. Further, the soft magnetic properties of SMCs were analyzed in detail. It is revealed that the annealed inorganic coating layer which predominantly consists of Al(PO 3) 3 , Al 2 O 3 , and P 2 O 5 exhibits a high resistivity, high temperature resistance and thin thickness, significantly reducing the eddy current loss. The outstanding magnetic properties of a power loss of 118.6 kW/m3 (100 kHz, 0.1 T) and permeability of 63.8 were achieved for this high-quality thin insulation coating. Moreover, the magnetic loss was separated into hysteresis, eddy current and excess part, and the mechanism was analyzed in detail. The reduced total loss can be ascribed to the suppression of the eddy current. The novel SMCs coating with K 3 PO 4 are particularly suitable for applications in high frequency and high DC bias situations for switching power supplies, photovoltaic inverter boost inductors and other applications. • Novel FeSiAl soft magnetic composites coated with K 3 PO 4 exhibited excellent temperature resistance. • The outstanding magnetic property with an ultra-low power loss of 118.6 kW/m3 (100 kHz, 0.1 T) was achieved. • The magnetic loss separation mechanism was analyzed in detail. [ABSTRACT FROM AUTHOR]

• A cellular model based on FEM is established to analyze the radiation characteristics of the magnetoelectric FBAR antenna. • A 1-D FDTD technique considering material losses is proposed. • Eddy current loss is affected by conductivity, clamped permeability, and film thickness. • Mechanical quality factors and piezomagnetic stress constant are the key parameters to determine the radiation efficiency. Bulk acoustic wave-mediated magnetoelectric (ME) antenna is the most promising acoustically actuated ultra-compact antenna scheme at ultrahigh frequency (0.3–3 GHz). However, the relevant research is still exploratory, and the antenna's multi-field coupling modeling and performance analysis are imperfect. This work presents a cellular model based on finite element simulation to analyze the radiation characteristics of the ME antenna integrated on a thin-film bulk wave resonator (FBAR). Compared with the finite difference time domain (FDTD) method, the cellular model has the advantages of simplicity and high universality. The effects of mechanical and dielectric losses of piezoelectric (PE) material and mechanical and eddy current losses of magnetostrictive (MS) material on radiation efficiency are analyzed through the intensive research of unit cells of four different material combinations. Results show that the mechanical quality factors and piezomagnetic stress constant are the key parameters to determine the radiation efficiency. Besides conductivity and permeability, eddy current loss is also closely related to the thickness of the MS layer. This study provides a theoretical foundation for enhancing the radiation performance of ME FBAR antennas and identifying areas for further development. [ABSTRACT FROM AUTHOR]

In this work, the minor alcohol was innovatively added to soften the hard phenolic-resin insulation shell which greatly improved the flowability of the core-shell (amorphous powder-insulating layer) particles during the molding process, effectively reducing damage to the coating and resulting in a higher density of powder cores (PC). Importantly, the permeability of the obtained PC was improved by 31 % at a softener content of 1.5 wt.%, and the corresponding core loss (50 mT, 100 kHz) was reduced by 45 % from 70.41 kW/m3 to 38.56 kW/m3. Moreover, the PC also exhibited improved DC bias and resistivity. Fundamentally, the high fluidity of the core-shell particles with alcohol softeners radically and effectively reduces the friction between the particles, thus improving the resistivity and reducing the air gaps in the PC, ultimately leading to lower eddy current losses and better magnetization. [ABSTRACT FROM AUTHOR]

For HEO@PPy composites, there are mainly eddy current loss and hysteresis loss in the high-entropy oxides. For the effect on the magnetic loss performance, it is weakening for Fe, Ni, and Co successively. The composite of HEO(1)-FeNi@PPy has the largest reflection loss with a minimum RL value of −32.04 dB and an effective absorption bandwidth of 5.8 GHz, and the corresponding thicknesses are almost the same, which enables the optimization of both parameters simultaneously. The sample also has the optimal waveband-thickness absorption characteristics. A reciprocal relationship was found between magnetic loss and dielectric loss. By incorporating the HEO(1)-FeNi@PPy powder into paraffin, it was found that the greater the amount of powder material, the higher the electric conduction loss and polarization loss, and the magnetic loss would decrease. The microwave frequency f was found to be the main variable affecting the magnetic permeability and dielectric constant. • The effect on the magnetic loss of HEOs is weakening for Fe, Ni, Co successively. • There is a reciprocal relationship between magnetic loss and dielectric loss. • Increasing HEO@PPy content can enhance the electric conduction loss and polarization loss, and decrease the magnetic loss. • Microwave frequency f is the main variable affecting the magnetic permeability and dielectric constant. [ABSTRACT FROM AUTHOR]

• A layer of hydrophobically modified nano-SiO 2 insulation layer was fabricated by DDS and TEOS as co-precursor. • The uniform insulation layer on the surface of Fe-Si-B-C powder not only further reduces the eddy current loss of AMPCs but also delays the growing of hysteresis loss. • The total energy loss of modified magnetic powder core was reduced by 16.1 % and 7.7 % at 1 MHz, 0.05 T compared to the raw powder core and TEOS hydrolyzed alone counterpart, respectively. The hysteresis effect and eddy currents caused by alternating magnetic fields greatly impede the improvement of the working efficiency and performance stability of soft magnetic powder cores. In this work, modified hydrophobic SiO 2 nanoparticles were prepared by tetraethyl orthosilicate (TEOS) and dimethyl-diethoxy-silane (DDS) as co-precursors through sol–gel methods. The effect of different proportions of DDS and TEOS on the amorphous magnetic powder cores performance was studied. It was demonstrated that the insulation layer in DDS and TEOS co-precursors hydrolyzed composite powders exhibited more uniform distribution compared with TEOS hydrolyzed alone counterpart. The introduction of methyl groups reduced the accumulation of hydrolysis intermediates on the surface of FeSiBC powders. Furthermore, the addition of DDS reduced eddy current loss significantly with a low hysteresis loss. The total energy loss of the DDS and TEOS co-hydrolysis powder core were reduced by 16.1 % and 7.7 % at 1 MHz, 0.05 T compared to the uncoated powder core and the TEOS hydrolysis alone counterpart, respectively. The presented results provide insights into improving the application range and energy utilization efficiency for the magnetic powder cores. [ABSTRACT FROM AUTHOR]

With the widespread use of digital systems and electronic communication devices, there is an urgent need to develop lightweight and efficient electromagnetic interference (EMI) shielding materials to address the growing problem of radiation pollution. RGO/MXene/Fe 3 O 4 aerogels were successfully designed and synthesised using a one-step hydrothermal process induced by an external magnetic field in this study. Reduced graphene RGO, MXene nanosheets and Fe 3 O 4 nanoparticles were suitably assembled together to achieve the combined advantages. The aerogels exhibited large specific surface area and hierarchical porosity. The material not only achieves an effective synergy between magnetic loss and dielectric loss, but also exhibits satisfactory EMI shielding performance. Magnetic field induced RGO/MXene/Fe 3 O 4 aerogels (MIRMFE-2) exhibits the best EMI shielding performance with an average SE T value of 76.9 dB. The excellent shielding performance of MIRMFE is attributed to both its 3D porous structure and the high dielectric loss due to multiple polarization relaxation, magnetic loss due to eddy current loss and natural resonance. The synthesis of MIRMFE provides an effective method for, designing high-performance and lightweight EMI shielding materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Mg B 2 superconducting material has a wide range of application prospects for its high transition temperature, favorable structural characteristics and low cost. When using Mg B 2 to produce superconducting energy storage magnets, it is necessary to twist superconducting wires into cables to increase their current carrying capacity. One typical cable is made of 6 Mg B 2 superconducting wires wrapped around 1 central copper wire, forming a (6+1) structure. Mg B 2 coils used for energy storage require solid impregnation and can be cooled by liquid hydrogen or solid nitrogen. Due to the need for fast charging and discharging of energy storage coils and low thermal conductivity of commonly used epoxy resin impregnation and solid nitrogen, it is necessary to consider the temperature variation characteristics caused by AC loss and eddy current loss during operation process. A coil with 8 turns in each layer and 4 layers is simulated using the (6+1)-structure cable. In order to obtain better temperature distribution results while reducing the time required for simulation operation, the simulation time is set to 1 s. The impact of epoxy resin properties and surrounding environments on the coil are then analyzed. The results indicate that increasing the thermal conductivity of epoxy resin can significantly reduce the maximum temperature of the coil, while only changing the cooling method is unhelpful in dealing with the problem of local overheating of the coil. • Epoxy resin affects the position with the highest temperature in a coil. • Cooling effects of static liquid hydrogen and solid nitrogen are almost the same. • Flow rate of liquid hydrogen is not helpful in avoiding coil overheating. [ABSTRACT FROM AUTHOR]

The loss effect in smart materials, the active part of a transducer, is of significant importance to acoustic transducer designers, as it directly affects the important characteristics of the transducer, such as the impedance spectra, frequency response, and the amount of heat generated. It is therefore beneficial to be able to incorporate energy losses in the design phase. For high-power low-frequency transducers requiring more smart materials, losses become even more appreciable. In this paper, similar to piezoelectric materials, three losses in Terfenol-D are considered by introducing complex quantities, representing the elastic loss, piezomagnetic loss, and magnetic loss. The frequency-dependent eddy current loss is also considered and incorporated into the complex permeability of giant magnetostrictive materials. These complex material parameters are then successfully applied to improve the popular plane-wave method (PWM) circuit model and finite element method (FEM) model. To verify the accuracy and effectiveness of the proposed methods, a high-power Tonpilz Terfenol-D transducer with a resonance frequency of around 1 kHz and a maximum transmitting current response (TCR) of 187 dB/1A/μPa is manufactured and tested. The good agreement between the simulation and experimental results validates the improved PWM circuit model and FEA model, which may shed light on the more predictable design of high-power giant magnetostrictive transducers in the future. [ABSTRACT FROM AUTHOR]

The A − φ − B magnetodynamic Maxwell system given in its potential and space-time formulation is a popular model considered in the engineering community. It allows to model some phenomena such as eddy current losses in multiple turn winding. Indeed, in some cases, they can significantly alter the performance of the devices, and consequently can no more be neglegted. It turns out that this model is not yet analytically studied, therefore we here consider its well-posedness. First, the existence of strong solutions with the help of the theory of Showalter on degenerated parabolic problems is established. Second, using energy estimates, existence and uniqueness of the weak solution of the A − φ − B is deduced. [ABSTRACT FROM AUTHOR]

A dual-stator Vernier permanent magnet (DSVPM) machine is proposed in this article for improving the power factor. Compared with the conventional single-stator Vernier permanent magnet (SSVPM) machine with the surface-mounted permanent magnet rotor, the proposed DSVPM machine has the higher power factor and the overload capacity. The reason for the higher power factor and the overload capacity in DSVPM machines is explained theoretically in this article by air gap permeance theory, and the advantages of the power factor and overload capacity of DSVPM machine are verified by the finite element analysis (FEA) through 18-slots and 34-poles SSVPM and DSVPM FEA model. The rotor eddy current losses, core losses and magnet demagnetization ratio of the DSVPM and SSVPM machines are also studied in this article, the FEA results reveal eddy current and core losses and magnet demagnetization ratio are all lower in the proposed DSVPM machine. The power factor of DSVPM machine variation with the magnet thickness and pole ratio (the ratio of the rotor pole pair number to the stator pole pair number) is also researched by the theoretical and FEA methods. In this article, a surface-mounted permanent magnet machine with fractional-slot concentrated-winding is designed to compare the torque density and cost with DSVPM machine. The sandwiched rotor structure of the proposed DSVPM machine is discussed and the structural analysis by three-dimensional FEA is carried out to prove the feasibility of rotor support, the result reveal that the rotor structure has the sufficient strength. [ABSTRACT FROM AUTHOR]

Fe-Si-Cr soft magnetic powder cores (SMCs), with high electrical resistivity, magnetic permeability, saturation magnetic induction, and good corrosion resistance, are widely applied to inductors, filters, choke coils, etc. However, with the development of electronic technology with high frequency and high power density, the relative decline in the magnetic properties limits the high-frequency application of SMCs. In this paper, the phosphating process and polyimide (PI) insulation coating is applied to Fe-Si-Cr SMCs to reduce the core loss, including hysteresis loss and eddy current loss. The microstructure and composition of Fe-Si-Cr powders were analyzed by SEM, XRD, and Fourier-transform infrared spectra, respectively. The structural characteristics of the Fe-Si-Cr @ phosphate layer @ PI layer core–shell double coating were studied, and the best process parameters were determined through experiments. For SMCs with 0.4 wt% content of PI, the relative permeability is greater than 68%, and the core loss is the lowest, 7086 mW/cm3; annealed at 500 °C, the relative permeability is greater than 57%, and the core loss is the lowest, 6222 mW/cm3. A 0.4 wt% content of PI, annealed at 500 °C, exhibits the ideal magnetic properties: μe = 47 H/m, P = 6222 mW/cm3. [ABSTRACT FROM AUTHOR]

A novel design method for the primary structure of a double-sided long-primary fractional-slot concentrated winding permanent magnet linear synchronous motor (DSLP-FSCW-PMLSM) is proposed in this article. Different from the traditional symmetric primary structure, the primary structure obtained by the proposed design method has two asymmetric primary cores and two asymmetric primary windings. This unique structure can reduce the variation of the flux density caused by the primary core slotting, and can effectively reduce the slot harmonic contents of the armature reaction magnetic field; thus, it can significantly reduce secondary eddy current losses. First, the basic structure is introduced. The air-gap magnetic field of permanent magnet and armature reaction are analyzed in detail. Second, the performance of the proposed motor is analyzed by means of three dimensional finite element method and compared with the traditional motor. The focus is on secondary materials, secondary eddy current losses, thrust, pole arc coefficient, magnet skew angle, and efficiency. Last, experiments are conducted on two prototypes of DSLP-FSCW-PMLSM. The validity of the proposed topology is verified by the test results of static thrust, back electromotive force, and armature reaction air-gap magnetic field. [ABSTRACT FROM AUTHOR]

FeNi/glass composites with 0 wt%,1 wt%, and 2 wt% glass content are produced, and their soft magnetic properties are systematically studied. The scanning electron microscope (SEM) results indicate that the FeNi particles are surrounded by glass powder. With the addition of glass powder, the saturation magnetization of the FeNi/glass composites decreases from 170 to 158 emu/g, and the effective permeability decreases from 56.1 to 39.1. With the increase of glass content, the imaginary part μ″ is reduced, indicating that the eddy current loss or excess loss is reduced at high frequency. The magnetic loss measurement results show that the addition of glass powder greatly reduces the eddy current loss. Furthermore, the FeNi/glass composite core with 2 wt% glass content has moderate permeability, higher quality factor Q, and better DC bias characteristics than other cores. The results show that the ideal glass powder content can improve the magnetic properties of FeNi composite materials, and glass powder can be used as an insulator in soft magnetic composites (SCMs). [ABSTRACT FROM AUTHOR]

An efficient method is proposed to predict eddy current loss of Litz wire coils, or completely transposed multi-strand coils, in transient finite element analysis (FEA). The method is based on analytical solutions of eddy current loss in a solid wire due to skin effects and proximity effects. The bundle of Litz or solid wires is homogenized by introducing a fill factor to describe the conducting area ratio. The analytical solutions in the frequency domain for round, square, and rectangular wires are further expanded to those in the time domain. The wire length direction in each 3-D mesh is automatically detected so that the flux density vector in each mesh can be correctly decomposed to the orthogonal and tangential components for anisotropic proximity effect loss computation. The method is applied to calculating eddy current loss of a gapped inductor in both 2-D and 3-D, and the results are compared with that using real solid wires. [ABSTRACT FROM AUTHOR]

Pulse width modulation current harmonics and space harmonics are some of the major factors affecting the rotor eddy current loss of the high-speed permanent magnet motor. In this study, based on the principle of the equivalent current sheet, a two-dimensional motor model in a rectangular coordinate system was established. Considering the armature reaction, the end effect, and the current harmonics generated by variable frequency power supply, the eddy current loss of the rotor at different frequencies was analyzed and calculated using the analytical and finite element methods (FEM). When the frequency is between 200 Hz and 600 Hz, the variation trend of the rotor eddy current loss with a frequency obtained by analytical calculation and FEM analysis is roughly the same, and the error is still within a reasonable range. However, as the frequency continues to increase, the error between the two becomes larger and larger. Furthermore, based on the two-dimensional FE model, the influence of the sleeve material, the thickness, and the composite structure on the rotor eddy current loss were studied and analyzed. It was found that adding a graphene shielding layer between the permanent magnet and the sleeve can effectively shield the harmonic magnetic field, greatly reduce the eddy current loss of the permanent magnet, and effectively prevent the temperature of the permanent magnet from being too high, which is conducive to the continuous and stable operation of the high-speed permanent magnet motor. [ABSTRACT FROM AUTHOR]

In high-speed and high-frequency electric machines, one of the major issues that impacts the performance and capability of a machine is the high-frequency eddy current losses in the windings. This work deals with AC winding losses in flat rectangular conductors. Aiming for eddy current loss mitigation, two different materials are investigated and compared for the same winding design, namely copper and aluminum. Using the finite element method (FEM), the conductor loss and current density behavior are simulated at the strand level. Further, in order to verify the simulated losses, the AC losses are measured and compared over a wide range of frequencies. Finally, recommendations are provided based on the obtained measurements to identify the best winding topology that is most suitable for automotive applications. [ABSTRACT FROM AUTHOR]

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Simulations of emergency states and tests of resistance of electrical devices to emergencies are performed in specialized high-power laboratories, the so-called short-circuit laboratories. For most electrical power devices, such measurements are required by international standards. The basic equipment of short-circuit testing laboratories consists of current transformers for measuring short-circuit currents. These transformers should not only enable the accurate conversion of sinusoidal currents—which is typical for conventional current transformers, but also asymmetrical short-circuit currents containing an aperiodic component, which classic current transformers cannot reproduce. Therefore, manufacturers and designers try to meet the market demands and design these special class 0.2 current transformers. To meet the high technical requirements, the field-circuit method with three-dimensional space–time analysis of electromagnetic fields was used during design, considering physical phenomena in ferromagnetic cores (i.e., hysteresis and eddy current losses) and the load of the secondary winding of the current transformer by the measurement system. The article presents simulations of secondary currents for the short-circuit current transformer model, and the results were confirmed by measurements and oscillograms of the currents flowing in the windings of the real model. The prototype of the designed short-circuit transformer meets the IEC/EN standard requirements. When measuring harmonic currents, the transformation errors meet the requirements of class 0.2. During the short-circuit current waveforms, the maximum instantaneous peak error does not exceed 1% of the error for all the subsequent maxima of the current waveform during the specified transient switching cycle. In comparison, the standard allows this error to be 10%. [ABSTRACT FROM AUTHOR]

The paper presents a study of the influence of magnetic hysteresis on macroscopic eddy current losses. Usually, this loss is calculated within many simplifying assumptions, of which the most striking is not only neglecting the hysteresis, but also the nonlinearity of the material. To check how such simplifications affect the results, the loss was calculated taking into account the hysteresis phenomenon for several materials. For this purpose, an algorithm for solving Maxwell's equations with magnetic characteristics given as a family of measured hysteresis loops was constructed. A new method for conversion between H and B fields using the measured hysteresis loops was also proposed. The results of calculations for three materials show that the eddy current loss calculated with magnetic hysteresis taken into account are smaller than those calculated via the classical formula obtained for linear materials. For the tested materials, the differences reach up to around 30%, depending on frequency, magnetic flux density and thickness of electrical sheet. This may result, among others, in erroneous determination of the excess loss in Bertotti's approach. [ABSTRACT FROM AUTHOR]

As a key component to ensure the safety and stability of the surface-mounted permanent magnet motor rotor, stress research on the sleeve has long been a subject that has attracted researchers. Fiber-reinforced composite materials have the characteristics of high specific strength, high specific modulus, and low eddy current loss. The use of a fiber-reinforced composite material sleeve that can effectively reduce the thickness of the sleeve and structural weight, and can improve the power density of the motor is an inevitable trend of the development of high-performance permanent magnet motors. This paper summarizes the matching of fibers and resins of composite materials to the sleeve: the stress design criteria, stress calculation method, and stress influencing factors of the composite sleeve; two typical stress-forming methods of the composite sleeve; and the preloading effect of the sleeve, strength, and rotor prototype performance testing. This paper focuses on the application of tension winding technology in sleeve forming. Based on the characteristics of composite material layer synthesis, this method has the advantages of high forming efficiency, small forming damage, easy realization of stress design, and a high preloading effect. This method can meet the sleeve-forming requirements of high-performance, large-scale, high-speed permanent magnet motors. However, the application of the new high-performance material system in the existing research is insufficient, the research on the technological factors in the tension winding process is scarce, and the performance testing method after the sleeve preparation is single, which needs further research. [ABSTRACT FROM AUTHOR]

In this paper, a novel cooling system of the yokeless and segmented armature axial flux machine (YASA) applied in‐wheel traction is presented. Although the cooling system has high cooling efficiency, it will deteriorate the electromagnetic characteristics of the motor. The eddy current analysis for the prototype is performed based on the 3‐D finite‐element method, and the distribution of eddy current in the cooling fins is presented. Through the 2‐D finite element analysis, the cause of the eddy current loss of the fin is revealed. In order to increase the output power of the motor, the height of the fin in the axial direction is optimised by the magneto‐thermal coupling method. And finally, the hub motor is manufactured and tested. It can be concluded that the measured data matched well with the analysis results. [ABSTRACT FROM AUTHOR]

It has advantages such as high power density and miniaturisation when the motor operates at high speed. However, as a side effect, the loss density is much higher than that of a constant speed motor. In addition, a retaining sleeve is inserted in the high‐speed motors to prevent the rotor from scattering. This insertion deteriorates the performance due to the increase of airgap, and eddy current loss occurs in the sleeve. In order to improve these shortcomings, the sleeve is redesigned in this paper. A groove was dug into the retaining sleeve and ferrofluid was injected. Ferrofluid refers to water or oil mixed with ultra‐fine powder. Since the permeability of ferrofluid is greater than that of airgap, it is possible to have high output and high efficiency. Since the material of the sleeve is non‐permeable, the performance is reduced with the same effect as increasing the airgap. However, if a ferrofluid is inserted by digging a groove in the retaining sleeve, the magnetic flux from the magnet flows into the stator through the ferrofluid, which has the same effect as reducing the airgap. Therefore, the torque density increases. Also, the eddy current loss is reduced through the retained sleeve groove. Moreover, a sleeve skew structure was used to further reduce the eddy current loss. In this paper, the mechanical rigidity at the rated speed was also taken into consideration. As a result, eddy current loss was reduced and torque density was improved. This is verified through the final finite element analysis. [ABSTRACT FROM AUTHOR]

This paper deduces an exact model of analytical calculation for the multilayer rotor eddy current losses of high‐speed permanent magnet machines based on the subdomain method. The analytical calculation model solution domain is divided into six parts of subdomains, including permanent magnet, shielding layer, metal retaining sleeve, air gap, slot openings, and windings. The Laplace equation of the air subdomain and the diffusion equation of the eddy current subdomain and the windings subdomain are established with the vector magnetic potential as the independent variable. The eddy current losses of the permanent magnet, shielding layer, and retaining sleeve of the multilayer rotor are calculated considering the slots effect and eddy current reaction. This analytical model is used to study the interfering factors of the multilayer rotor eddy current losses including the shielding layer thickness, carrier ratio, and modulation ratio. Finally, the correctness and regularity of the analytical calculation model are proved by finite element analysis and machine experiment analysis. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

To effectively minimize magnetic losses and increase the efficiency of machines, particularly transformers, exact separation of total losses in the magnetic cores of electrical appliances into hysteresis and eddy current is required. To address this issue, the author proposes three variants of the wattmeter method, based on different dependences of eddy current and hysteresis losses on the magnetization reversal frequency, magnetic flux, and temperature, referring to the methods of two frequencies, two densities, and two temperatures. Two experiments were performed for each of the three methods under different conditions. In no-load experiments at two frequencies, at two magnetic flux densities, and two temperatures of the magnetic core, the active powers spent on heating the core were measured, and expressions for the powers of hysteresis and eddy current losses were obtained. The experimental results obtained using different methods are consistent with each other. The advantages and difficulties of each method are analyzed. The combination of methods determines the degree of density index for the magnetic flux in the hysteresis loss power expression (Steinmetz factor) in a particular transformer. [ABSTRACT FROM AUTHOR]

Aiming at the problem that the vibration calibration accuracy is seriously affected by the additional dynamic magnetic field interference and eddy current effect of the electromagnetic vibration exciters, a suppression method based on magnetic field tracking compensation is proposed. The influence of the dynamic magnetic field interference of the driving current on the total harmonic distortion of the driving coil output electromagnetic force waveform and the characteristics of the eddy current effect are studied. The compensation current set on the central yoke, its direction opposite to the driving current, to realize the dynamic tracking compensation and suppression of the additional dynamic magnetic field interference and eddy current loss of the driving coil, and effectively improve the vibration waveform accuracy and eliminate the temperature change of the working platform caused by eddy current effect. The simulation results show that the eddy current loss may be reduced by 53 % and the total harmonic distortion of the driving electromagnetic force waveform may be reduced by 0.12 % though the method in this paper. [ABSTRACT FROM AUTHOR]

Core losses of transformers motivate many engineers and scientists to design and implement different transformers for their specific aims. Since there exists a growing interest on high frequency applications in today's world, design and optimization studies of a magnetic fluid core transformer (MFCT), having an easy and cheap production approach in high frequency applications, are considered in the present paper. The desired design should operate in a more efficient way within a wide frequency band. The MFCT considered here can be a solution to the eddy currents and core losses encountered in the conventional transformers with its low conductivity, oil-based magnetic fluid and super paramagnetic characteristic. The magnetic fluid in the proposed work consists of a combination of ferromagnetic particles made by iron in an averaged diameter of 70 μm with an adjustable magnetism compared to the traditional magnetic fluids and an engine oil, thereby the magnetic permeability of the overall fluid core can be fully adjustable by the variation of mass proportion between the oil and iron powder as an easy process without any chemical process. A COMSOL Multi-Physics design is performed via a finite element package in three dimensions. It is proven that the iron particles exhibit a complicated pattern inside the engine oil and produce a well-defined high frequency output at the secondary windings in a wide range of frequency. [ABSTRACT FROM AUTHOR]

The inclusion of a high energy density permanent magnet into magnetic gear improves the machine's torque density. However, it also contributes to eddy current loss, especially in a high-speed application such in electric vehicle. In this paper, the losses from eddy current and iron loss are investigated on concentric magnetic gear (CMG). Torque multiplier CMG is designed with 8/3 gear ratio for this study. Iron loss and eddy current loss are compared and discussed. Based on this study, eddy current loss contributes to almost 96% of the total loss. This finding is hoped to direct the researcher to focus more on reducing loss associated with eddy current loss. [ABSTRACT FROM AUTHOR]

Capacitive power transfer (CPT) uses an electric field as the transfer medium to achieve wireless power transfer (WPT). Benefitting from the low eddy current loss, simple system structure and strong plasticity of the coupling coupler, the CPT system has recently gained much attention. The CPT system has significantly improved transfer power, system efficiency, and transfer distance due to continuous research and discussion worldwide. This review briefly presents the basic working principle of the CPT system and summarizes the theoretical research in four aspects, including coupling coupler and high-frequency power converter. Following this, the review focuses on research in six key directions, including system modelling and efficiency optimization. The application of CPT technology in five fields, including medical devices and transportation, is also discussed. This review introduces the progress of CPT research in recent years, hoping to serve as a reference for researchers, to promote the further research and application of the CPT system. [ABSTRACT FROM AUTHOR]

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To accurately predict the eddy current loss of silicon steel laminations over broadband frequency range, an improved parametric magneto dynamic model (IPMD) is proposed in this paper. According to the nonuniform distribution of magnetic field in the cross-section of the silicon steel lamination under high-frequency magnetization, the analysis area of the lamination is divided into several slices by nonlinear segmentation, wherein each slice the magnetic field distribution is regarded as uniform. Meanwhile, to accelerate the calculation speed of the IPMD model, the relationship between skin depth and slice number is deduced and verified. Furthermore, the Tellinen (TLN) hysteresis model is used when implementing the IPMD model to further increase the accuracy of eddy current loss calculation. [ABSTRACT FROM AUTHOR]

In recent years, wireless power transmission (WPT) technology based on magnetic resonance has been extensively studied. However, in contrast to that in the air, wireless power transmission in seawater medium will be accompanied by inevitable energy loss, that is, eddy current loss (ECL), which will increase with the frequency and coil current. In this article, an equivalent circuit model of the eddy current loss of underwater wireless power transmission is established, two methods to reduce the eddy current loss are proposed, and the optimal modulus ratio for the coil current of the dual-coil wireless power transmission system to reduce eddy current loss is calculated. Electromagnetic field (EMF) simulation software verifies the correctness of the two methods, and it is concluded that increasing the phase difference of the coil current or controlling the coil current ratio to ensure that the optimal modulus ratio is in a certain range can reduce the eddy current loss effectively and improve the energy transmission efficiency of the system by about 4~5%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hollow ZnFe 2 O 4 microspheres decorated NRGO magnetic composite foams were prepared. • Ultralight NRGO/ZnFe 2 O 4 composite foams had a 3D hierarchical porous structure. • Microwave absorption performance was modulated by regulating annealing temperature. • Strong absorption and broad bandwidth under an ultrathin thickness were achieved. • The underlying microwave dissipation mechanisms of composite foams were proposed. Magnetic graphene foams with three-dimensional (3D) porous structure, low bulk density and multiple electromagnetic loss mechanisms have been widely recognized as the potential candidates for lightweight and high-efficiency microwave attenuation. Herein, zinc ferrite hollow microspheres decorated nitrogen-doped reduced graphene oxide (NRGO/ZnFe 2 O 4) composite foams were prepared via a solvothermal and hydrothermal two-step method. Results demonstrated that the attained magnetic composite foams possessed the ultralow bulk density (12.9–13.5 mg·cm−3) and 3D hierarchical porous netlike structure constructed through stacking of lamellar NRGO. Moreover, the microwave dissipation performance of binary composite foams could be notably improved through annealing treatment and further elaborately regulating the annealing temperature. Remarkably, the attained composite foam with the annealing temperature of 300.0 °C presented the integrated excellent microwave attenuation capacity, i.e. the strongest reflection loss reached −40.2 dB (larger than 99.99% absorption) and broadest bandwidth achieved 5.4 GHz (from 12.4 GHz to 17.8 GHz, covering 90.0% of Ku-band) under an ultrathin thickness of only 1.48 mm. Furthermore, the probable microwave dissipation mechanisms were illuminated, which derived from the optimized impedance matching, strengthened dipole polarization, interfacial polarization and multiple reflection, notable conduction loss, natural resonance and eddy current loss. Results of this work would pave the way for developing graphene-based 3D lightweight and high-efficiency microwave absorption composites. [ABSTRACT FROM AUTHOR]

A broadband three-dimensional (3D) hexagonal periodic structured gypsum absorber incorporated with carbon black (CB) was designed and fabricated, and the effects of geometric parameters and CB mass fraction on the electromagnetic (EM) wave absorption performance were simulated and measured in 2–18 GHz. The simulation and experimental results exhibit that the effective bandwidth for reflection loss (RL) under – 10 dB can cover the whole frequency ranges of 2–18 GHz. The appreciable agreement between simulation and experiments testifies the validity of the well-designed gypsum absorber. The broadband absorption performance can be attributed to the synergistic effect of structural design and material characteristics. The impedance matching condition can be significantly improved due to the periodic structural design, and most incident EM waves can be attenuated by the multiple reflections and diffractions effects induced by 3D periodic hexagonal arrays and eddy current loss, conductivity loss and dielectric polarization loss caused by CB particles. It is believed that the proposed 3D periodic hexagonal structured gypsum absorber has great potentials in military and civilian applications to avoid radar detection and solve EM radiation pollution. [ABSTRACT FROM AUTHOR]

When the wireless power transfer (WPT) system is installed on the autonomous underwater vehicle (AUV), there is a non-negligible eddy current loss around the coupler. The existence of the ferrite core causes the nonlinear distortion of the magnetic field, which makes the design of the WPT coupler more complicated and difficult. In this paper, the key parameters that affect the performance of the coupler were obtained through calculation and finite element analysis (FEA). Then, the coupler was parametrically modeled in Maxwell, and the Non-dominated Sorting Genetic Algorithm (NSGA-II) was used to optimize its design, considering two objective functions: mutual inductance and equivalent coupler loss impedance (ECLI). Finally, twenty groups of Pareto optimal points were evaluated using the Technique for Ordering Preferences by Similarity to Ideal Solution (TOPSIS) method. Five groups of design points with different weights were screened out. The effectiveness of the optimization process was verified by comparing the optimization results with the initial results. [ABSTRACT FROM AUTHOR]

In this work, we studied the effects of iron-deficient compositions on the phase formation, morphology, grain growth, and magnetic property of BaTi1.2Co1.2Fe9.6−xO19−σ (x = 0.4, 0.6, 0.8, 1.0) hexagonal ferrites. The X-ray diffraction(XRD) experiment results indicate that the magnetic sample with iron deficiency content (0.6 ≤ x ≤ 1.0) consists of only the magnetoplumbite phase while the hematite (α-Fe2O3) phase is observed in the x = 0.4 sample besides the main magnetoplumbite phase. The scanning electron microscope (SEM) results indicate that the average grain size gradually first decreases, and then increases again with the iron deficiency content (x) from 0.4 to 1.0. The influence of iron deficiency on the magnetic properties of ferrites was systematically studied. With the increase of iron deficiency content, the initial magnetic permeability (μi) and saturation magnetization (Ms) first increase to their maximum and then decrease. Hc decreases with the increase of the iron deficiency content (x) from 0.4 to 1.0. As the number of iron deficiency increases, hysteresis and eddy current losses first decrease and then increase. The results suggest that the optimal iron deficiency can reduce the eddy current and hysteresis loss in the BaTi1.2Co1.2Fe9.6−xO19−σ system. [ABSTRACT FROM AUTHOR]

Ni0.27Cu0.10Zn0.63AlxFe2−xO4 (x = 0.0–0.16 with step 0.02) bulk ceramics were prepared from sol–gel-synthesized nanocrystalline powders and sintered at 1100 °C and 1250 °C, respectively. Rietveld refinements of the XRD data confirm the single-phase nature of the prepared ceramics with cubic spinel structure. Lattice parameter, cell volume, density, crystallite size, and grain size decrease with increasing Al content. The dynamic electrical and dielectric study has been carried out over 100 Hz to 100 MHz at room temperature (RT). The decreasing nature of ε * with a rising field shows the frequency-dependent regular dielectric behavior of the synthesized ceramics. The ε * magnitude increases several times with increasing sintering temperature due to elevated grain growth. The tan δ varies remarkably with Al content and explained with Koop's phenomenological view of dielectrics. The lower tan δ magnitude (~ 0) reveals the high-frequency potentiality of the prepared ceramics. Electric modulus study ensures the non-Debye relaxation mode in each ceramic composition. The complex impedance spectra sketch the popular Cole–Cole plots and demonstrate the active contributions of grain and grain boundary resistances (Rg and Rgb) on electrical characteristics. Both the Rg and Rgb increase with Al substitution in many compositions reducing the eddy current losses and disperse more technological versatility for multifunctional appliances. The frequency-dependent conductivity obeys the Jonscher's universal power law and presents three different conduction processes, long and short-range translational hopping as well as localized or re-orientational hopping motion at RT. [ABSTRACT FROM AUTHOR]

This article proposes a mesh-based magneto-electric coupling network model for prediction and reduction of permanent magnet (PM) eddy current loss in a flux-switching permanent magnet machine. The key is to couple the electromagnetic inductions between the eddy current network and the equivalent magnetic network (EMN) in stator PMs dynamically. First, the eddy current networks of PMs are established with electric meshes. The electromotive forces of electric mesh are induced by considering double-side effects based on Maxwell's equations. Second, the stator meshing method is propose with PM segments, and combined in the EMN matching to the eddy current mesh. High efficiency and accuracy with detailed magnetic field distributions can be obtained. Then, the magnetic fields generated from EMN PM nodes are coupled in eddy current network to accurately predict the flow directions and density distributions. Finally, the original design and two other structures with rotor magnetic barriers are analyzed for reduction of eddy current losses. The effectiveness of the proposed model is verified by finite-element analyses and experimental results. [ABSTRACT FROM AUTHOR]