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In this work, SEM images analysis and fractal dimension calculations are performed on the fracture surfaces for N50-type with low coercivity, 30 EH-type with high coercivity, and isotropic Nd-Fe-B permanent magnets. It is discovered for the first time that the difference between the fractal dimensions of fracture surface parallel and perpendicular to the c-axis D ∥ and D ⊥ for N50-type magnet with low coercivity is large, and the difference between the fractal dimensions of D ∥ and D ⊥ for 30 EH-type magnet with high coercivity is small. However, there is almost no difference in the fractal dimension of D ∥ and D ⊥ for isotropic magnet. The correlation between anisotropic fractal dimension of the fracture surface and coercivity is revealed. The difference between the fractal dimension of fracture surface D ∥ and D ⊥ not only reflects the difference in micro morphology, but also serves as an important performance parameter to characterize the coercivity of the magnet, which provides new insights for studying the relationship between the magnetic properties and the microstructure of permanent magnetic materials.

In order to give full play to the potential of Nd-Ce-Fe-B magnets and increase the coercivity of magnets with a fixed average composition, the influence of the cooperation effect of anisotropy field and magnetostatic field on their coercivity was studied. Micromagnetic simulations revealed that neither the most heterogeneous composition distribution nor the most homogeneous composition resulted in the highest coercivity. This is due to the variation in a critical field H crit which quantifies the cooperation effect of anisotropy field and magnetostatic field. By subtly changing the composition distribution of the Nd-Ce-Fe-B magnets, this work provides a new perspective for further improvement of the coercivity. This adjustment modifies the anisotropy field distribution and the magnetostatic field distribution.

It is confirmed that the solid solution temperature range to obtain optimal magnetic properties is different for the magnets with different Fe contents, and the correlation between magnetic properties and microstructures influenced by solid solution temperature (Ts) has been systematically studied. The optimal solid solution temperature range is 1413–1463 K for the Sm(CobalFe0.213 Cu0.073Zr0.024)7.6 magnet, which is higher than that of the Sm(CobalFe0.262Cu0.073Zr0.024)7.6 magnet (1403–1453 K), and the optimal Ts range is about 50 K for both of the magnets. The solid solution temperature range shifting toward relatively high temperature is due to the increase in a phase transition temperature. The magnet solution-treated at proper temperature exhibits 1:7H single phase, and intact cell structure and high Cu concentration (23.12 at%) in the cell boundary are found after aging process, which makes the magnet shows high intrinsic coercivity (Hcj) and magnetic field at knee-point (Hknee). At a lower solid solution temperature, the 2:17H, 1:5H and Zr-rich precipitation phases appear, which affects the cell structure, density of lamellar phase and Cu concentration in the cell boundary, leading to the reduced magnetic properties. However, at a higher solid solution temperature, there exist obviously light gray and dark regions with different Sm, Cu and Fe contents in scanning electron microscopy observation, and the magnet shows low pinning field in the two regions and incomplete cell structure, resulting in an inferior Hcj and Hknee.

Busbar current sensor without magnetic core is used more and more in compact power electronic equipment due to its small size and lightweight. The differential measurement technique is generally adopted to resist external magnetic interference. The sensitivity of busbar current sensors varies with the frequency of the sensed current due to the skin effect in the busbar. Traditional coreless busbar current sensors can accurately measure dc current, but the measurement error increases when sensing high-frequency ac current. A coreless sensor configuration based on four tunneling magnetoresistance (TMR) chips is proposed in this article with high measurement accuracy for both dc and high-frequency ac currents while eliminating the effect of magnetic stray field. An optimization method is introduced for the layout of the TMR chips around the busbar in order to obtain a current error below 1.5% up to 1 kHz. The effectiveness of the proposed sensor configuration and layout optimization method are verified by finite element simulation and prototype tests.

It is confirmed that phase homogenization is very important for improving the magnetic properties of 2:17-type Sm–Co sintered magnets. In this work, the influence of solid solution process on microstructure and magnetic properties of the Sm(CobalFe0.233Cu0.073Zr0.024)7.6 sintered magnets was systematically studied. With the solid-solution treating duration (ts) increasing from 0 to 4 h, intrinsic coercivity (Hcj) increases from 12.83 to 36.54 kOe, magnetic field at knee-point (Hknee) increases from 2.76 to 19.14 kOe, and the maximum energy product increases from 19.79 to 29.48 MGOe. The electron probe microanalyzer results reveal that there mainly exist gray and dark regions besides “white” rare earth-rich phase, and the content of Sm, Fe and Cu elements for the two kinds of regions changes a lot for the specimens. Furthermore, with ts increasing up to 4 h, the elements content deviation between the gray and dark regions becomes small gradually from 3.94 at% to 0.27 at%, 7.66 at% to 0.21 at% and 7.27 at% to 0.16 at% for Sm, Fe and Cu elements, respectively. Moreover, transmission electron microscopy results show that the distribution of cell size is much more concentrated for aged specimens when ts is 4 h. It is also found that the Cu concentration at cell boundaries for the 4 h solid-solution treatment case shows relatively higher values and greater concentration gradient (1.94 at%/nm). It is verified that sufficient solution treatment duration is prerequisite to form these homogeneous microstructural features, which are the key points for obtaining both high Hcj and Hknee.

In this article, the phase compositions, microstructures, and magnetic properties of PrNd-free Ce-Fe-B-based sintered magnets with the nominal composition of (Ce0.78Y0.17La0.05)16.28Febal.B7.44M1.94 (at.%: M = Co, Al, Cu, and Nb) have been investigated. It shows that a lamellar crystalline structure is formed in the Ce-Fe-B-based strip casting (SC) alloy. The Y-substituted Ce-Fe-B-based SC alloy is mainly composed of R2Fe14B and RFe2 phases. It suggests that Y substitution is helpful for depressing the $\alpha $ -Fe phase generated in the SC alloy. The island-like intermediate phases exist in the RFe2 region, which are probably caused by the incomplete peritectic reaction during alloy solidification. The Curie temperature $T_{\mathrm {c}}$ of the Y-substituted Ce-Fe-B-based alloy is about 463 K, which is higher than that of the Ce2Fe14B compound ( $T_{\mathrm {c}} =424$ K). For the experimental Ce-Fe-B-based sintered magnet without PrNd addition, the remanence $B_{\mathrm {r}}$ of 8.31 kG, the coercivity $H_{\mathrm {cj}}$ of 0.92 kOe, and the maximum energy product (BH)max of 5.30 MGOe have been obtained. A good combination of coercivity $H_{\mathrm {cj}}$ (= 5.57 kOe) and maximum energy product (BH)max (= 20.17 MGOe) has been achieved in the Ce-Fe-B-based blended magnet with PrNd/ $\sum $ RE = 25% prepared using a binary main phase (BMP) method. The heterogeneous elemental distributions and microstructure characteristics of the BMP magnet are also analyzed.

Made available in DSpace on 2022-04-28T19:50:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-01-01 There is an ever-increasing requirement for higher power vibrating platforms to test large-scale structures. Whilst this may be achieved with a single shaker, this is an expensive option. An alternative solution is to drive a platform with two or more smaller shakers. To do this effectively, however, requires the identical amplitude and phase response of the shakers. In practice, due to manufacturing tolerances and uneven loading, this is not possible without a control system. The design and implementation of such a system is the objective of this paper. An adaptive FxLMS algorithm is used in the synchronous control of a dual-shaker system, considering the dynamic coupling between the shakers. A simulation is presented to verify the effectiveness of the control algorithm before the control system is integrated with practical a dual-shaker system driving a vibrating platform. It is shown that there are significant differences between the controlled and the uncontrolled system, demonstrating the efficacy of the control approach. College of Power and Energy Engineering Harbin Engineering University Department of Mechanical Engineering UNESP Department of Mechanical Engineering UNESP

Sintered (Ce, Nd)-Fe-B magnets with high cost performance were prepared by substituting of Ce for Nd with the dual-main phase method. The corrosion behaviors of dual-main phase sintered (CexNd1–x)30Fe69B1 (x = 0.15 wt%, 0.3 wt%) magnets, which were named as Ce15 and Ce30, were studied in 3.5 wt% NaCl, 6.6 wt% Na2SO4 and 3.0 wt% NaOH aqueous solutions, respectively. The galvanic corrosion of Ce30 is stronger than that of Ce15. However, the mass loss value of Ce30 is smaller than Ce15 after free corrosion for 33 d in NaCl solution. In the other two solutions, all the results show that the corrosion resistance of Ce30 is better than that of Ce15. The scanning electron microscope results show that the crack and shedding of the magnetic phase of Ce30 is less than that of Ce15. Combined above, the abnormal corrosion behavior shows that Ce30 magnets perform better corrosion resistance than Ce15, and the degradation degree of magnetic phase mainly affects the corrosion resistance of magnets.

Sintered permanent magnets based on domain-wall-pinning-type Sm2Co17 have recently attracted considerable attention due to their low-temperature coefficient, excellent high-temperature magnetic properties, and remarkable oxidation and corrosion resistances. However, the relationship between the knee-point coercivity, $H_{\mathrm {k}}$ , and the microstructures of these Sm2Co17-based bulk magnets has not been widely studied. Therefore, herein, sintered permanent magnets with nominal compositions of Sm(CobalFe0.227Cu0.070Zr0.023) z ( $z =7.40$ , 7.47, 7.54, 7.61, and 7.84) (at.%) were prepared via conventional powder metallurgy, and their magnetic properties were investigated. The results showed that as $z$ increased from 7.40 to 7.84, $H_{\mathrm {k}}$ first increased and then decreased. The maximum optimal $H_{\mathrm {k}}$ of 1717 kA $\cdot \text{m}^{-1}$ (21.58 kOe) corresponded to the magnet with dimensions of ~52.8 mm $\times49.2$ mm $\times36.6$ mm, a maximum magnetic energy product ( BH )max of 232 kJ $\cdot \text{m}^{-3}$ (29.1 MG $\cdot $ Oe), and $z =7.61$ . The transmission electron microscopy revealed that the crystalline structure and chemical composition of the magnet are the two main factors determining $H_{\mathrm {k}}$ .

MM85Cu15 (MM = La, Ce, Pr, Nd) eutectic alloys were added into the hot-deformed Nd-Fe-B magnets to enhance the coercivity. It is found that three endothermic peaks occur on the differential scanning calorimetry curve of the MM-Cu melt-spun ribbons at 432.2, 451.1 and 516.5 °C. The peaks substantially correspond to three types of MM-Cu low-melting eutectic phase. The coercivity of magnets increases when the MM-Cu content is lower than 4 wt%, and then keeps almost no change with the content further increasing to 5 wt%. The coercivity of the hot-deformed magnets with 4 wt% and without MM-Cu addition is 948 and 683 kA/m, respectively. Nearly all the platelet-shaped grains are isolated by the thickened intergranular phase after MM-Cu addition. Moreover, the average grain size of the magnets with MM-Cu addition decreases compared with that of the magnet without MM-Cu addition. Scanning electron microscopy images show that the areal fraction of the RE-rich grain boundary phase increases from 8.6% to 15.1% after MM-Cu addition. The La, Ce together with Cu and Ga aggregate at the grain boundary regions separating neighboring grains and smoothing the grain boundaries. Therefore, both the thickened grain boundary and decreased mean grain size result in the enhancement of coercivity after MM-Cu eutectic alloy addition.

The vibration and noise produced by the powertrain and waves inside ship cabins limit working efficiency and crew and passengers’ accommodation quality. This paper simplifies ship cabins as cavities and explores active control techniques to attenuate sound transmission via multiple parallel-supported flexible subplates. The theoretical formulations of the interaction between multiple subplates and cavities were performed and the coupling relationships between them were analyzed. Based on the multiple subplates and the cavity coupling models, numerical simulations were performed using the derived optimal controller to minimize the transmission of sound into the cavities through two and nine parallel-supported subplates. The various control strategies were explored to minimize the coupling system’s acoustic potential energy, and the control performances were compared and discussed. The mechanism of reducing sound transmission through multiple supported subplates into a cavity is revealed. The simulation results showed that the vibration pattern of the controlled subplate is changed after it is regulated, which increases its radiation to subdue the other subplates’ radiation, while increasing vibration of the controlled subplate. The more subplates a cavity has, the more kinetic energy the controlled subplate possess. Furthermore, the noise reduction performance of a cavity with fewer subplates is better than that with more subplates.

Large dc current is typically measured by an open-loop sensor without a magnetic core. The widely used configuration uses a differential magnetic sensor inserted into the busbar hole or a differential magnetic sensor placed on the upper and lower surfaces of the busbar. The use of a differential sensor has the advantage of being resistant to external magnetic fields. In this article, a new differential ultra-small magnetic sensor with the size of 23.2 mm × 16.5 mm × 7.2 mm is designed. The sensor is based on tunneling magnetoresistance (TMR) and is placed on the upper surface edge of the busbar. The supply voltage is 5 V, the rated current measurement range is ±150 A, and the peak current measurement range is ±250 A, corresponding to 2.5 ± 2 V output at ±250 A dc peak current. The relative accuracy is less than ±1% at 25 °C and is less than ±2% over the full temperature range from -40 °C to 105 °C.

In this paper, dependence of magnetic properties on microstructure and composition of Ce-Fe-B sintered magnets with Cu-doped Ce-rich alloy addition was investigated. It shows that the maximum energy product (BH)max and coercivity Hcj of Ce-Fe-B sintered magnet are improved from 6.76 to 9.13 MGOe by 35.1%, and from 1.44 to 1.67 kOe by 16.0%, respectively, via adding 5 wt% liquid phase alloy of Ce35.58Fe57.47Cu6B0.95 (at%). Compared with the magnet without Ce-rich alloy addition, the volume fraction of the grain-boundary phase with low melting point increases in the magnet with Ce-rich alloy addition, which is beneficial to improving the microstructure and promoting the coercivity enhancement of the magnet. In the Ce-Fe-B magnet with Ce-rich alloy addition, Cu and Ce enrich in the grain boundaries of the magnet after annealing, therefore the as-annealed magnet has a higher coercivity than the as-sintered magnet. A distinct Fe-rich layer with the average thickness of 60 nm is found in the grain boundaries in the magnet without Ce-rich alloy addition, but it seems that Fe-rich phase disappears in the magnet with Ce-rich alloy addition. The present work suggests that the further improvement of coercivity in the Ce-Fe-B sintered magnets is expectable by designing the composition and structure of added liquid phase alloys.

To apply bulk hot-deformed magnets into commercial fields, it is quite necessary to deeply understand the origins and evolution of their inhomogeneous microstructure. In this work, the microstructure of hot-deformed nanocrystalline cylindrical Nd-Fe-B magnets with a dimension of ∼24.8 mm in diameter and ∼7.0 mm in height along the radial direction was investigated in order to correlate them with the inhomogeneous magnetic properties. The remanence was 1.42 T, 1.37 T, and 1.30 T for the samples taken from the center (sample P3), subcenter (sample P2), and edge (sample P1) of the hot-deformed magnet, respectively. Scanning electron microscopy images showed from the P3 to P1 the interval of strip-shaped Nd-rich layers increased. Meanwhile, the perpendicularity between the pressure direction and the Nd-rich layers deteriorated for the samples from the P3 to P1. Well oriented platelet-shaped grains with c-axis parallel to the pressure direction were observed in the P3 sample, and the orientation gradually deteriorated with the position changing from the center to the edge. It was also found that large Nd-rich phase aggregation areas occurred in the edge sample. The maximum value of Henkel plot decreased gradually for the samples from the P3 to P1, which was caused by the thickened grain boundary observed by transmission electron microscopy. The openness of recoil loops increased gradually from the center to the edge due to the aggregation of the Nd-rich phase. The inhomogeneous microstructure shows distinct effects on magnetic properties, therefore changing the magnetization behavior along the radial direction of hot-deformed magnets.

Ce-based magnets have attracted extensive attention in both academia and industry due to their excellent property–price ratio and distinctive phase structures. Characteristically, Ce-based sintered magnets have widely tunable magnetic properties with changing Ce contents. Therefore, they can be used to meet many different application requirements from packaging market to driving motors, etc. The intrinsic magnetic properties, phase composition, and microstructures of the Ce-based sintered magnets with different Ce contents have been summarized. The service performances such as temperature stability, corrosion resistance, mechanical properties and thermal expansion of commercial Ce-based sintered magnets are introduced. The research and development trends of the Ce-based magnets in the future are pointed out.

Individual grains with diverse dimensional parameters were introduced to investigate the magnetization reversals in anisotropic Nd2Fe14B magnets. The micromagnetic simulations were carried out via Object Oriented MicroMagnetic Framework (OOMMF). With the same bottom area and height, analysis results show that the coercive fields for different bottom shapes are of similar values. Designed as a cubic grain, the coercive field presents descending tendency as grain volume ascends. Under constant grain volume, with aspect ratio increasing, the coercive field decreases in the beginning and increases soon. Based on the demagnetization field vector, the effects of bottom shape, grain volume and aspect ratio on the coercive field can be explained. The nucleation point is chosen to discuss. Its synthetic field and reversal field are calculated by parallelogram law and inverse external field equation, respectively. The synthetic field equal to the reversal field is defined as critical field, which always shows the same tendency as the coercive field for all cases of this study. It can be concluded that critical field is qualified to be a reference index to measure the magnitude of coercive field.

The numerical simulation model of single roller melt spinning for rapid quenching process of NdFeB alloy was built, and the vacuum chamber, cooling roller and sample were taken into account as a system. The existing mature technology was in order to verify the correctness of simulation. The rapid quenching ribbons with different roll speeds were used as the simulation objects. The results of the numerical simulation and experiments show that the validity of the model has been testified and the reasons of the formation of complete quenching ribbons and by-product have been explained. The experimental thickness of the ribbons is proportional to the theoretical thickness. In the same spray condition, with the roll speed increasing, the thickness decreases linearly. At the speed range of 25–30 m·s−1, the simulated calculation date is close to the experimental date, which can be considered as an ideal technological parameter.

In this article, the phase constitution, microstructures and melting points of Ce35.58Fe63.47-xAlxB0.95 alloys (at.%; x = 0, 3, 5, 10) have been investigated. It indicated that the Ce-rich alloy with x = 0 was mainly composed of CeFe2, Ce2Fe17 and γ-Ce phases. The AlCe3 phase was found in the alloy with x = 3. The microstructures and phase distribution characteristics of the alloys have obviously changed with increasing Al content (x = 5,10). The volume fractions of CeFe2 and Ce2Fe17 decreased. Some dispersed Ce-Al eutectic structures with low melting point were found in the alloy with x = 10. It is showed that the melting points of Ce-rich alloys have a decreasing tendency with increasing Al content, the melting points reduced from 942 °C at x = 0–856 °C at x = 10. Furthermore, the influences of the Ce35.58Fe53.47Al10B0.95 alloy addition on the microstructures and magnetic properties of sintered Ce-Fe-B magnets, were also discussed. The remanence Br slightly decreased, while the intrinsic coercivity Hcj, maximum energy product (BH)m and squareness Hk/Hcj (the ratio of knee coercivity to intrinsic coercivity) of the magnets had significant improvements, and these indexes increased by 8%, 22%, 24%, respectively.