Demagnetization Of Magnets Research Articles

Demagnetization analysis of an 18GHz electron cyclotron resonance ion source permanent magnet hexapole.

An upgrade of ECR2 at the Argonne Tandem Linac Accelerator System is under way, focusing on increasing the intensity capabilities of the facility. ECR2 is a room temperature electron cyclotron resonance ion source, and the upgrade has strict requirements to retain radial access to the plasma chamber and keep the ion source operating without the use of superconducting magnets. The upgrade design with respect to the magnet arrangement and magnetization vectors has recently been presented [R. C. Vondrasek, J. McLain, and R. H. Scott, J. Phys.: Conf. Ser. 2743, 012044 (2024)] using the same magnetic material as the current ECR2 hexapole. A thorough exploration of the demagnetization potential of this hexapole was carried out, and the risk of demagnetization was deemed too high, despite the magnetic performance meeting the requirements for the upgrade. Additional permanent magnet materials are considered with their respective performance evaluated. Magnet strength and demagnetization resistance are investigated and optimized with the final room temperature design demonstrating a high temperature transient demagnetization resistance and a radial magnetic field of 1.18T at the plasma chamber wall. The simulations of this hexapole suggest that it will be sufficient to optimize intensity with a 14.5GHz driving frequency and will allow 18GHz operation, while keeping a high safety margin for maintaining magnet performance.

Performance Comparison Between Microstepping and Field-Oriented Control for Hybrid Stepper Motors

With their cost-effective manufacturing process, hybrid stepper motors (HSMs) are a popular choice for position control in low-power industrial applications. These versatile motors offer a compelling solution for reducing system costs and size since at standstill/low speeds, HSMs typically have higher torque density with respect to low-power permanent magnet (PM) motors. This higher torque density determines a reduced use of rare-earth PMs and, therefore, a lower environmental footprint. In practical applications, the commonly used microstepping control faces low efficiency, low dynamic performance, vibrations, and a variable maximum continuous torque depending on the working point. In this paper, the operating region of an HSM is extended in the field-weakening (FW) region, showing how field-oriented control (FOC) with FW allows one to strongly increase the drive performance with a slight cost increase thanks to the availability of low-cost magnetic encoders. Due to the fact that FOC provides only the requested current, the HSM faces lower temperatures, lower insulation degradation, and lower permanent magnet demagnetization issues. An experimental evaluation comparing the commonly used microstepping and the proposed FOC with FW is performed on four commercial HSMs with different DC voltage power supplies using an industrial test bench. In particular, the experimental campaign has a focus on steady-state conditions in the case of the maximum continuous torque, showing the advantages of FOC with FW because the advantages in transient conditions are well known.

Surrogate Modeling for Drive Co‐Simulation Including Local Irreversible Demagnetization Knowledge

ABSTRACTIn order to survey possible local demagnetization of permanent magnet drives during transient operations and/or faulty functioning in case of multi‐phase drives, co‐simulation including converter, vector control, and finite element model could be investigated. Nevertheless, expensive simulation time limits practically this solution. To solve this problem, the paper proposes a surrogate model of an electrical machine taking into account locally the irreversible demagnetization effect. In case of a multi‐phase machine working in transient operations and irreversible demagnetization, the proposed surrogate model gives large benefit in computational time in comparison with an finite element approach.

Analysis of Permanent Magnet Demagnetization during the Starting Process of a Line-start Permanent Magnet Synchronous Motor

Neodymium (NdFeB) rare earth Permanent Magnets (PMs) are widely used in the manufacturing of Line-Start Permanent Magnet Synchronous Motors (LSPMSMs). During the initial startup of LSPMSMs, irreversible PM demagnetization often occurs. This research provides a thorough examination of the PM demagnetization process during the initiation of a 15-kW, 3000-rpm LSPMSM, which was converted from a squirrel-cage Induction Motor (IM) featuring a 3-bar PM. Utilizing Ansys/Maxwell2D software for simulations and conducting experiments, this study reveals that upon starting the LSPMSM, demagnetization occurs at the two outermost PM pairs. This leads to unstable motor operation at synchronous speed, significant current fluctuations, and a substantial decrease in performance. The findings suggest that to ensure effective LSPMSM operation, it is crucial to either restrict frequent restarts or select an appropriate PM type to prevent partially irreversible demagnetization, thereby enhancing power efficiency.

Liquid Metal Leaching for Rare Earth Magnet Recycling

This study investigates the optimization of liquid metal leaching for recycling rare earth elements (REEs) from NdFeB magnets, a critical step in addressing the increasing demand for these materials in various high-tech applications. We explored the effects of leaching time, stirring, and magnet demagnetization on the yield of the leaching process using molten magnesium. Conducted at 900 °C, our experiments assessed the leaching process over periods of 2, 3.5, and 5 h, with and without the application of stirring. Our findings show that longer leaching times considerably increase neodymium (Nd) and praseodymium (Pr) leaching yield, with a notable peak in efficiency found at 5 h. Stirring improved the uniformity of REEs significantly and resulted in up to 80% yield. Furthermore, our data show that pre-leaching magnet demagnetization improves leaching specificity, significantly reducing the presence of non-target metals like nickel and copper. These insights offer a pathway to more cost-effective recycling of REEs from magnet scrap, which is essential for environmentally conscious management of resources amid the escalating global demand for REEs.

Theoretical and Numerical Modeling of Optical Switching of Epitaxial Nanostructures Based on Iron-Garnet Films

The paper presents a theoretical analysis of magnetization switching in a gadolinium ferrite garnet film due to the demagnetizing effect of a femtosecond laser pulse. Using the Lagrange formalism for a two-sublattice ferrimagnet, the effective Lagrangian, thermodynamic potential, and Rayleigh dissipative function are obtained. The phase diagram of the ferrite film is analyzed, and the main states of the system are identified. Magnetization switching diagrams and trajectories of the order parameter dynamics of the magnet are constructed. The ranges of magnetic fields, temperatures, and demagnetization values for the most efficient magnetization switching are analyzed.

An integral sliding-mode observer-based equivalent-input-disturbance method for fault-tolerant control of permanent magnet synchronous motor drive system

Aiming at the problem of the control performance degradation of a permanent magnet synchronous motor (PMSM) drive system due to permanent magnet demagnetization, which is caused by mechanical vibration and high temperature, this paper presents an equivalent-input-disturbance (EID) fault-tolerant control method based on an integral sliding-mode observer (ISMO). The mathematical model of a PMSM with demagnetization fault in dq-axis coordinate system is first established. Then, the model is transformed into an EID system one. An ISMO is used to estimate the state variables of the EID system and an equivalent-input-demagnetization fault. The estimate of the equivalent-input-demagnetization fault is compensated in a feed-forward manner. Thus, the fault-tolerance control of PMSM demagnetization is achieved. Finally, the stability analyses of the ISMO and the entire EID system are given. The comparative results of a hardware-in-the-loop experiment show that the designed method effectively improves the fault-tolerant control performance of a PMSM drive system with demagnetization fault.

Detection of Demagnetization Faults in Electric Motors by Analyzing Inverter Based Current Data Using Machine Learning Techniques

Demagnetization of the rotor magnets is a significant failure mode that can occur in permanent magnet synchronous machines (PMSMs). Early detection of demagnetization faults can help change system parameters to reduce power output or ensure safety. In this paper, the effects of demagnetization faults were analyzed both in simulation and experiments using the example of drone motors. An approach was investigated to detect even minor demagnetization faults that does not require any additional sensing effort. Machine learning (ML) techniques are used to analyze the phase current data directly received from the inverter to enable anomaly detection. For this purpose, the phase current is transformed by the Fast Fourier Transform (FFT), the spectral data is then reduced in dimensionality, followed by an anomaly detection algorithm using a one-class support vector machine (OC-SVM). To ensure simplified initialization of the ML model without the need for training sets of damaged drives, only data from magnetically undamaged motors was used to train the models for anomaly detection. Different selections of considered harmonics and different metrics were investigated using the experimental data, achieving a precision of up to 99%, a specificity of up to 98%, and an accuracy of up to 90%.

Optimization of Nd-Fe-B permanent magnet guideways with high-temperature stability

High-temperature superconducting (HTS) pinning Maglev systems are advantageous due to their ability to achieve large-scale passive-stabilized levitation. Elevated temperatures can lead to a reduction in the magnetic characteristics of the permanent magnet guideway (PMG), which may pose a risk to the safe functioning of HTS Maglev trains. In order to guarantee the secure and dependable functioning of HTS Maglev trains, it is necessary to augment the high-temperature stability of the PMG. This study involves simulating the high-temperature stability of present PMGs and developing a new PMG that exhibits greater performance. Magnetic field simulation is employed to compute the demagnetization of permanent magnets (PMs) in several typical PMGs, encompassing both reversible and irreversible scenarios, in order to examine the factors contributing to demagnetization and evaluate the thermal stability of the PMGs at elevated temperatures. The grade, size, and magnetization direction of the Halbach-type PMG are subsequently optimized and compared to the original Halbach-type PMG. Following this, ideas for further optimization are provided. The optimized Halbach-type PMG reduces the overall decay ratio of the highest magnetic flux density Bz by 5.77% compared to the existing Halbach-type PMG. Additionally, the irreversible decay ratio is decreased by 6.13% at 85 ℃. The levitation force decay ratio on the HTS bulks above the optimized Halbach-type PMG is decreased by 8.11% compared to the existing Halbach-type PMG. Additionally, the irreversible decay ratio is reduced by 9% at 85 ℃. This study provides valuable insights for enhancing the efficiency and performance of PMGs and HTS Maglev trains over extended periods of operation.

Perpendicular magnetic anisotropy of Cr/CoFeB/MgO modulated by MgO thickness

The dependence of perpendicular magnetic anisotropy (PMA) on the MgO thickness in Cr/CoFeB/MgO/Ta films has been experimentally investigated. A clear PMA is observed in the as-deposited samples with 1.8 nm MgO while no as-deposited PMA is shown in those with 4.0 nm MgO. This may be attributed to the moderate oxidation degree of CoFeB and larger interfacial anisotropy energy density K i to overcome the volume magnetic anisotropy and demagnetization field. On the contrary, samples with 4.0 nm MgO demonstrate PMA only after annealing, which might be due to the oxygen and boron diffusion during the annealing process. These results would provide a method to optimize the design of CoFeB/MgO structures on 3d metals for future applications in perpendicular magnetic devices.

Elevated temperature magnetic microstructures and demagnetization mechanism for grain boundary diffused dual-main-phase (Nd, Ce)-Fe-B magnets

The combination of dual-main-phase (DMP) (Nd, Ce)-Fe-B magnets and grain boundary diffusion process (GBDP) is currently a research topic for obtaining high-cost performance materials in rare earth permanent magnet fields. The novel structural features of GBDP (Nd, Ce)-Fe-B magnets give a version of different domain reversal processes from those of non-diffused magnets. In this work, the in-situ magnetic domain evolution of the DMP magnets was observed at elevated temperatures, and the temperature demagnetization and coercivity mechanism of the GBDP dual-main-phase (Nd, Ce)-Fe-B magnets are discussed. The results show that the shell composition of different types of grains in DMP magnets is similar, while the magnetic microstructure results indicate the Ce-rich grains tend to demagnetize first. Dy-rich shell with a high anisotropic field caused by GBDP leads to an increase in the nucleation field, which enhances the coercivity. It is found that much more grains exhibit single domain characteristics in the remanent state for GBDP dual-main-phase (Nd, Ce)-Fe-B magnets. In addition, the grains that undergo demagnetization first are Ce-rich or Nd-rich grains, which is different from that of non-diffused magnets. These results were not found in previous studies but can be intuitively characterized from the perspective of magnetic domains in this work, providing a new perspective and understanding of the performance improvement of magnetic materials.

Non-invasive rotor temperature detection of magnetically levitated turbo molecular pump based on high-frequency inductance

The rotor temperature has a significant effect on the reliable operation of the magnetically levitated turbo molecular pump (MLTMP). Therefore, it is crucial to monitor the rotor temperature during the operation of the MLTMP to prevent irreversible demagnetization of the permanent magnet and improve production efficiency. However, direct measurement of rotor temperature is a challenge due to the complexity of installing a temperature sensor on the high speed spindle. This paper presents a non-intrusive method for detecting rotor temperature based on high-frequency(HF) inductance estimation. On this basis, a novel method is proposed that injects a HF rotating voltage into the stationary coordinate frame and introduces synchronous demodulation to achieve accurate estimation of the HF inductance. Finally, the experimental results conducted on the MLTMP test bench indicate that the proposed method can effectively detect the rotor temperature, and the temperature error is within 3 ∘C.

Loss And Temperature Rise Analysis of Permanent Magnet Motor Based on Magneto-thermal Coupling Field

Because of the situation of motor performance degradation caused by permanent magnet demagnetization and increased loss of built-in permanent magnet synchronous motor under high temperature working conditions, this paper optimizes the rotor magnetic circuit structure of the motor and uses amorphous alloys. The material stator core replaces the original ordinary silicon steel stator core to suppress the motor temperature increase and reduce the motor loss. Through simulation, comparative analysis and calculation, the result could show that losses and temperature increase are significantly reduced after optimization. Finally, temperature rise testing was conducted on the prototype, confirming the correctness of the improved model.

High Effective Permeability and Low Power Loss of FeSiAl/Al2O3/ZnO SMC for High Frequency Application

AbstractSoft magnetic composites (SMCs) are key materials in electronic devices. Conventional SMCs incorporate too much insulating material in order to reduce eddy current loss at high frequency, resulting in severe magnetic dilution and demagnetization field, which leads to deterioration of the magnetic performance. In this paper, ZnO precursor is homogeneously deployed on the surface of FeSiAl, which in situ generates a thin and dense Al2O3 layer on the surface of FeSiAl through the interfacial solid phase reaction between Al and O atoms during annealing process. Meanwhile, ferromagnetic ZnO layer is simultaneously obtained due to the loss of O. The formed Al2O3/ZnO layers effectively reduce power loss and endow high frequency stability with less influence on effective permeability. Finally, FeSiAl/ZnO‐0.4% SMC exhibits low power loss of 83.2 mW cm−3 (50 mT/100 kHz), high effective permeability of 92, and cut‐off frequency as high as 40 MHz. This study provides an efficient route for high performance SMCs and broadens high frequency application of soft magnetic devices.

An approach to solving the effect of background in fluidized bed on electromagnetic tomography

As a non-invasive measurement technique, electromagnetic tomography (EMT) system based on tunneling magneto resistance (TMR) can detect the distribution of medium in the gas–liquid–solid fluidized bed by the difference of permeability. The distribution of medium in the three-phase fluidized bed is not uniform, and the solid clusters and bubble clusters are formed in the background of the gas–liquid–solid mixture. Since the effect of the background in the pipe of the fluidized bed on the boundary measurement data of the TMR-EMT system is much greater, it is difficult to detect solid clusters and bubble clusters when the image is reconstructed directly using the boundary measurement data. In order to improve the detection of clusters by the TMR-EMT system, a method to weaken the effect of the background is proposed. The equivalent magnetic circuit model is used to estimate the background permeability. Then the magnetic dipole theory and demagnetization effect theory are utilized to establish a simple background compensation model based on the estimated background permeability. Using the compensation model, the effect of the background is weakened from the boundary measurement data and the cluster distribution information is highlighted. Simulation and experimental results demonstrate the effectiveness of the proposed method.

Enhancement of local anti-demagnetization ability of permanent magnet by selected area grain boundary diffusion toward high-speed motors

The working environment of permanent magnets in high-speed motors is harsh, because they are seriously affected by multi-physical fields such as temperature, stress, weak magnetic control field, etc., and irreversible demagnetization is easy to occur under the extreme working conditions. In this work, a model of high-speed Interior Permanent magnet Motor is established, the easy demagnetization area of the permanent magnet is simulated by electromagnetic and thermal simulations to determine, and its local anti-demagnetization optimization is performed. Dy/Tb co-infiltration is carried out in the easy demagnetization region of the permanent magnets, and the process of selective zone diffusion is analyzed based on the principle of selective zone grain boundary diffusion. Through microscopic observation and macroscopic magnetic performance test, the effect of local anti-demagnetization performance enhancement of the optimized permanent magnets is verified. The results show that the magnetic properties of the optimized permanent magnets are obviously improved after the optimization of the selected zones. The present approach is important for the follow-up less heavy-rare-earth research of permanent magnet and its application in high-speed motors.

Electromagnetic–Thermal Characteristics Analysis of a Tubular Permanent Magnet Linear Generator for Free-Piston Engines

Temperature rise of the tubular permanent magnet linear generator (TPMLG) might lead to insulation failure and demagnetization of permanent magnets, affecting the safe and stable operation of other equipment and the entire system. Herein, a bidirectional electromagnetic–thermal coupling method for analyzing the electromagnetic loss and thermal characteristics of a TPMLG considering the effect of increased temperature on the permanent magnet was proposed. To study the electromagnetic–thermal characteristics of the TPMLG under stable power generation, a two-dimensional electromagnetic field model and a three-dimensional temperature field model were established and coupled. The temperature field of the TPMLG was numerically calculated using computational fluid dynamics over finite volume method under natural air cooling and forced air cooling conditions. Effects of loss and air flow velocity on the steady temperature field were investigated. Results indicated that copper loss increased by 24.5% considering the influence of temperature rise. The windings’ top central position in the TPMLG was the spot with the highest temperature of 127.8 °C and there was a potential demagnetization risk for the permanent magnets. Some reference for future research of clarifying thermal characteristics and cooling design was provided.

Permanent magnet synchronous motor demagnetization fault diagnosis based on leakage radial magnetic density

A method of demagnetization fault diagnosis of permanent magnet synchronous motors is proposed by measuring the radial magnetic density of the leakage field at the external space point of the motor. The method enables non-invasive diagnosis of motor permanent magnet demagnetization faults compared to other methods. In this paper, an analytical model of the radial magnetic density of the leakage field of a surface-mounted permanent magnet synchronous motor under no-load conditions is proposed, and its accuracy is verified by simulation. The influence mode of demagnetization fault on the radial magnetic density of the leakage field is analyzed, which provides a new idea for the diagnosis of motor demagnetization fault.

Study on magnetic properties and demagnetization process of the c-plane in the grain boundary diffusion magnet

Grain boundary diffusion (GBD) can effectively increase the coercivity of sintered Nd-Fe-B magnets. Tb is deposited in the specific areas of the c-plane rather than the entire c-plane to reduce the amount of heavy rare earth elements. In this work, we investigate the magnetic properties and demagnetization process of the c-plane using experimentation and micromagnetic simulation. The c-plane is divided into the center area without Tb deposition and the edge area with Tb deposition. According to the results of the experiment and micromagnetic simulation, it has been found that diffusion on the edge area can decrease the amount of Tb by 58% and increase the contribution of Tb to coercivity (ΔHcj/wt.% Tb) to 20.55 kOe/wt.%. Compared to the other areas on the c-plane, diffusing on the edge area offers the vast majority of Hcj for the GBD and has the highest ΔHcj/wt.% Tb. Diffusing a small amount of Tb onto the center area can supplement the remaining Hcj. Micromagnetic simulation and Magneto-optical Kerr microscopy are used to study the differences in magnetic properties among different areas on the c-plane by simulating the demagnetization process. Because the edge area is more likely to be demagnetized than the center area, the diffusion of Tb in the edge area can significantly strengthen Hcj.

Giant Low-Field Cryogenic Magnetocaloric Effect in a Polycrystalline EuB4O7 Compound.

To deal with the shortage and high price of helium-3 resources, adiabatic demagnetization refrigeration technology as an alternative to helium-3-based refrigeration technology has received much attention. The magnetism and ultralow-temperature magnetocaloric effect (MCE) of the EuB4O7 compound have been investigated. The results of magnetic and quasi-adiabatic demagnetization measurements suggest the absence of a magnetic order above 0.4 K for EuB4O7. The dipolar interaction between the nearest-neighbor Eu atoms has a characteristic energy of about 800 mK, which may induce a large MCE. The maximum magnetic entropy change reaches 22.8, 36.2, and 47.6 J·kg-1 K-1 at μ0H = 0-10 kOe, 0-20 kOe, and 0-50 kOe, respectively. Measurements by a quasi-adiabatic demagnetization device show that the lowest temperature achievable (289 mK) for polycrystalline EuB4O7 is lower than that (362 mK) for the commercial refrigerant Gd3Ga5O12 (GGG) single crystals. The hold time is more than 70 min below 700 mK, with an environment temperature of 2 K, proving that EuB4O7 exhibits superior cooling performance.