Demagnetization Methods Research Articles

Retracted: Fault Diagnosis Method of Rotor Magnetic Field Local Demagnetization in Permanent Magnet Synchronous Motor Model Predictive Current Control System

Retracted: Fault Diagnosis Method of Rotor Magnetic Field Local Demagnetization in Permanent Magnet Synchronous Motor Model Predictive Current Control System

Study of magnetoelastic demagnetization of locally magnetized steel

To improve the accuracy of determining mechanical stresses in steel by the method of magnetoelastic demagnetization (magnetoelastic memory), the magnetoelastic sensitivity of the material to elastic stresses is additionally measured by applying or removing an additional load of a known value. We present the results of studying the magnetoelastic demagnetization of locally magnetized steel by varying stresses of the uniaxial tension or compression against a background of the base load. The magnetoelastic sensitivity of the steel in a loaded state to variable stresses has been assessed. It is shown that the determination of the magnetoelastic sensitivity of the steel to variable loads makes it possible to improve the accuracy of estimating base stresses in the steel structure using magnetoelastic methods. It is revealed that a decrease in the strength of the magnetic scattering field of the local residual magnetization (LRM) of the steel after variable loading (or unloading) exponentially depends on the magnitude of the base stresses. The possibility of controlling the uniaxial mechanical stresses in steel structures in the magnetoelastic memory mode which is based on the dependence of the strength of magnetic scattering field of the local residual magnetization of the steel on the uniaxial stresses is shown. A method for monitoring uniaxial stresses in the elements of steel structures by the method of magnetoelastic memory is proposed using the measured magnetoelastic sensitivity of the material. The results obtained can be used in the development of a method for monitoring the stress-strain state of steel structures during operation under the simultaneous effect of static and dynamic loads.

New magnetostratigraphy constrains in the southern Paraná magmatic province (Herveiras and Gramado Xavier areas), Rio Grande do Sul state, South Brazil: Implications for the timing between volcanic sources

This paper undertakes a new paleomagnetic study of 51 lava flows that crop out in Southern Paraná Magmatic Province. The volcanic rocks are basalt of low-Ti content type (18 flows) and Palmas silicic type (33 flows) corresponding to the Caxias do Sul, Barros Cassal, and Santa Maria sub-types covering all lithostratigraphic units of the region. This study is part of a broad magnetic study in the Brazilian part of the Paraná-Etendeka LIP to understand the temporal relationship between the volcanic units of different compositions allowing the investigation of the contemporary nature of the multiple sources. The characteristic remanent magnetization (ChRM) for the lavas was obtained by alternating field (a.f.) and thermal demagnetization methods, and is interpreted as a thermo-remanent magnetization carried by stable pseudo-single domain magnetite grains, being acquired during the cooling of the lava flows. The high-quality of the ChRM results from both areas allows us to interpret that the emplacement of all volcanic rocks was geologically very fast, as verified by the symmetrical direction of both polarities (normal and reverse i.e. positive reversal test) of the geomagnetic field associated with the stratigraphy of all lava flows. The passage from pahoehoe to rubbly basalts was marked by a change of polarity of the geomagnetic field. Our results suggest that all volcanic rocks were emplaced by at least two volcanic events as shown by the polarity changes, and the sources of basaltic and silicic rocks of different compositions were active at the same time.

An Active Controllable Demagnetization of Closed-Loop HTS Magnet and its Distributed 2.5D H-Model

Closed-loop high temperature superconducting (HTS) magnets have great potential to be used in many fields due to their abilities to be operated in persistent current mode. However, in emergency rundown, they are required to get demagnetized actively and controllably. In this paper, an active controllable demagnetization of closed-loop HTS magnet by flux pump with thermal switches is proposed and investigated. The Joule heat dissipated and the transport current in the magnet during demagnetization is calculated numerically. Besides, in order to improve the calculation speed, a distributed 2.5D H-model of the magnet is suggested, in which the computing tasks are divided into two coupled parts: a 3D model and a 2D axisymmetric model, and are deployed on two different computing nodes. Experiments are carried out to verify the rationalities of the introduced demagnetization method and the distributed 2.5D H-model. The results shows that the proposed demagnetization method can realize active-controlled demagnetization of a closed-loop HTS magnet rapidly without generating too much heat, and, compared with H formulation, the suggested model can effectively reduce the calculation time.

Solid‐state heteronuclear multiple‐quantum spectroscopy under a magic‐angle spinning frequency of 150kHz

AbstractWe hereby demonstrate that1H detected15N‐1H heteronuclear multiple‐quantum spectroscopy can be carried out at a magic angle spinning frequency of 150 kHz. While the15N‐1H multiple‐quantum coherences can be directly excited from the dipolar order created by the method of adiabatic demagnetization in the rotating frame, it is technically more advantageous to acquire the chemical shift evolution of the heteronuclear multiple‐quantum coherence by two separate chemical shift evolution periods for1H and15N. We also show that the heteronuclear multiple‐quantum correlation spectrum can be obtained by shearing the corresponding heteronuclear single‐quantum correlation spectrum.

Apparent undisturbed paleoposition of mid-Cretaceous plutons emplaced across a Jurassic island arc segment in the southernmost part of the Peninsular Ranges batholith, Baja California, Mexico

The Calmallí (CA), Piedra Blanca (PB), and El Barril (EB) plutons were emplaced during the Late Cretaceous at the southern limit of the Peninsular Ranges batholith (PRB) at the present latitude of ∼28°N. These plutonic suites are juxtaposed, showing contrasting compositions, probably associated with different basement rocks. The region is separated by the high magnetic values in the western zone compared with the lowest magnetic values in the eastern zone. The western CA pluton intrudes a Jurassic island arc assemblage, whereas host rocks outcrops of the PB and EB are absent, but it is inferred that they intruded into the eastern margin of the Jurassic arc. The CA plutonic suite has a ca. 100 Ma old mafic core surrounded by ca. 102–105 Ma old tonalities. Such zonation is a typical feature of many plutons of the western PRB. The PB and EB plutons show granodioritic to granitic compositions of ca. 92 Ma. We compare the paleoposition of the CA-EB section with respect to the San José, and San Pedro Mártir plutons (∼31°N), and the Compostela pluton (∼29°N) which yield clockwise rotations of 31°–45°, and 16.4°, respectively. These northern plutons record rotations by tectonic deformation at suture zones between the Alisitos island arc and the older North America craton. Based on the paleomagnetic observations in the transition zone between western and eastern type plutons, we analyzed 15 sites from the CA, nine from the PB, and 23 from EB to evaluate their paleoposition. We obtained the characteristic remanent magnetizations (ChRM) following the detailed stepwise alternating magnetic field (AF) and thermal demagnetization methods. Each pluton was compared to the reference pole of North America at 100 Ma and 90 Ma. The paleopoles do not differ much from the cratonic references since the data indicate an apparent clockwise rotation of 8.1° ± 8.8° and a flattening of −13.9° ± 10.6° for CA pluton and an apparent clockwise rotation of 1.43° ± 8.3° and −14.2° ± 9.8° of flattening for combined paleopole of PB and EB plutons. Statistically, the paleopoles displacement are not significative, similar to five cretaceous plutons located NNW of the study area, suggesting that the mid-Cretaceous plutonic suites of the southern PRB remained stable since their emplacement in a period between 128 Ma and 90 Ma.

Rapid Demagnetization of New Hybrid Core for Energy Harvesting

This paper presents the results obtained using the rapid demagnetization method in the case of an NdFeB magnet and a new hybrid core. The developed core consists of three basic elements: an NdFeB magnet, Terfenol-D, and a specifically developed metallic alloy prepared by means of a suction casting method. The main goal of proposing a new type of core in the event of rapid demagnetization is to partially replace the permanent magnet with another material to reduce the rare-earth material while keeping the amount of generated electricity at a level that makes it possible to power low-power electrical devices. To “capture” the rapid change of magnetic flux, a small number of coils were made around the core. However, the very low voltage level at very high current required the use of specialized electronic transducers capable of delivering a voltage level appropriate for powering a microprocessor system. To overcome this problem, a circuit designed by the authors that enabled voltage processing from low impedance magnetic circuits was used. The obtained results demonstrated the usefulness of the system at resonant frequencies of up to 1 MHz.

A record of the lower Mammoth geomagnetic polarity reversal from a marine succession in the Boso Peninsula, central Japan

SUMMARY Palaeomagnetic records from geological archives provide significant information about the nature of geomagnetic polarity reversals; however, there are few detailed palaeomagnetic records of pre-Pleistocene reversals. The lower Mammoth Subchron boundary (late Pliocene) is recorded in a 10-m interval of a marine succession deposited at high accumulation rates (9–66 cm kyr–1) in the Boso Peninsula, central Japan. Here, we report a continuous palaeomagnetic record of the lower, normal to reverse boundary interval of the Mammoth Subchron, including the geomagnetic field direction and relative palaeointensity, with an average temporal resolution of ca. 800 yr. A hybrid method of thermal demagnetization at 200 °C and progressive alternating field demagnetization were used to effectively extract the primary palaeomagnetic component, which is carried by magnetite. The lower Mammoth transition is characterized by palaeomagnetic direction of instability and decay of the relative palaeointensity, and occurred from late Marine Isotope Stage MG3 (3351 ka) to MG2 (3336 ka) or MG1 (3331 ka), spanning 15–20 kyr. Virtual geomagnetic poles (VGPs), calculated from primary palaeomagnetic directions, rapidly rebounded twice from southern latitudes to northern latitudes within the transition. In contrast to the complex lower Mammoth reversal behaviour recorded in the Boso Peninsula succession, records from a lava sequence in O'ahu (Hawai'i) reveal a rebound following a 180° directional change, and those from a marl succession in Sicily (Italy) indicate a single rapid directional change. Diverse geomagnetic field evolution among these three sections is reflected resolution difference among the records likely in combination with an influence of non-axial dipole field.

An approach to the transformer core residual magnetism evaluation and demagnetization

Aiming at the problem of transformer inrush current suppression, a method of transformer core residual magnetism evaluation and demagnetization is proposed. Firstly, by setting the amplitude and time of DC current, different transformer core residual magnetism states are obtained. Secondly, under different residual magnetism conditions, the high-voltage winding of the transformer is charged and discharged in the forward and reverse direction alternately. The current change data in the process is collected, and the correlation coefficient of the current data in the forward and reverse charging processes is calculated, which represents the transformer core residual magnetism states. Finally, the DC current with alternating change direction and gradually decreasing amplitude is applied at the high voltage winding to demagnetize, and the variation of residual magnetism is analyzed during the demagnetization process.

Fast and Complete Mitigation of Residual Flux in Current Transformers Suitable for Auto-Reclosing Schemes Using Jiles-Atherton Modeling

Accurate measurement of electrical currents cannot be done when the core of current transformers (CTs) is saturated. One of the reasons that causes saturation of a CT is the activation of the auto-reclose function for the circuit breaker. When the circuit breaker is switched off, a residual flux will remain in the CT core, and when the circuit breaker is reconnected, this residual flux may cause saturation of the CT core. It is necessary to remove the residual flux in an auto-reclosing scheme. In the auto-reclosing scheme, due to the short time interval between each reclosing shot of the circuit breaker, only methods that have a high-speed operation should be used to mitigate the residual flux to prevent CT core saturation. This paper introduces a fast and complete demagnetization method based on Jiles-Atherton magnetic modeling to mitigate the residual flux in the CT core. The advantages of this method are high-speed performance, independent of the CT characteristics, high accuracy and high reliability against the secondary open circuit. To evaluate the efficacy of the proposed method, software simulations and laboratory experiments are performed on a 63kV, 300A/5A CT. The results are presented and analyzed.

Пристрій розмагнічування установки магнітної дефектоскопії осі колісної пари

У статті показана необхідність та визначені і проаналізовані основні способи розмагнічування деталей і виробів, виконаних з феромагнітних матеріалів. За результатами порівняльного аналізу обрано і обґрунтовано спосіб розмагнічування осі колісної пари, заснований на циклічному перемагнічуванні синусоїдальним постійно змінюваним магнітним полем з плавно спадною до нуля амплітудою. Запропоновано пристрій розмагнічування, що реалізує даний спосіб і забезпечує якісне розмагнічування осі на підставі визначення її магнітного стану з подальшим коректуванням величини поля, що розмагнічує.

Review of Permanent Magnet Lifting Technology

Permanent magnet lifting technology refers to the knowledge of the process of magnetic material suction unloading and transfer through permanent magnet lifting device with strong magnetic material as magnetic field energy. Compared with the traditional electromagnetic lifting device, the permanent magnet lifting device attracts and lifts ferromagnetic objects through the magnetic force of strong magnetic permanent magnet materials without excitation current during the lifting operation. Therefore, the permanent magnet lifting device has the advantages of energy saving, reliable use, low cost and high weight absorption ratio. This paper introduces the development of permanent magnet lifting technology, including the working principle and design problems of permanent magnet lifting device. According to the different demagnetization methods, it can be divided into electromagnetic demagnetization type lifting permanent magnets and mechanical demagnetization type lifting permanent magnets. Finally, the prospect of permanent magnet lifting technology is prospected and suggestions for its development are put forward.

Avoid Current Transformer Saturation Using Adjustable Switched Resistor Demagnetization Method

In some conditions, the flux in the core of current transformers (CT) increases. If this increase in flux leads to saturation of the protective core, it can create a lot of problems in power system protection. One of the hardware solutions to prevent the occurrence of core saturation in CT is the fixed switched resistor demagnetization method. Due to disadvantages such as dependence on CT parameters and inefficiencies in severe core saturation, the use of this method has not been expanded. This paper proposes a new method to improve the fixed switched resistor demagnetization method. In the proposed method, instead of using a fixed resistor in the circuit topology, an adjustable resistor with an auxiliary transformer is used. In the previous method, the control process is based on flux estimation from the secondary terminal voltage. The control process in the proposed method is based on the second derivative of CT secondary current. To verify the effectiveness of the suggested method, first simulation is done using COMSOL and MATLAB softwares and then all necessary electronic and control circuitry are designed and built. Experimental test is carried out on a 20 kV- 500/5 A CT. The simulation and experimental results show that this method prevents the CT from saturation in case of short circuit faults. The main advantages of this method are independent to CT parameters and efficient in severe core saturation.

Isothermal Remanent Magnetization (IRM) and Direct Current Demagnetization (DCD) Curves for Nanocrystalline Sm-Y-Co Alloys

Magnetization curves were measured using the methods of isothermal remanent magnetization (IRM) and direct current demagnetization (DCD) for nanocrystalline Sm0.5Y0.5Co5 alloys. The study of magnetic properties for nanocrystalline Sm0.5Y0.5Co5 alloys was performed with the Physical Property Measurement System (PPMS). The alloys exhibited a high remanent coercivity of 2.1 MA/m. The ratio of magnetic susceptibilities for nanocrystalline Sm0.5Y0.5Co5 alloys was χd/χr = 4.6, indicating the presence of magnetic interactions in the alloys. Nanocrystalline Sm0.5Y0.5Co5 alloys with magnetic interactions were studied by measuring ΔM curves against the magnetic field, and the alloys showed dipolar and exchange interactions.

MODERN PROBLEMATICS AND ANALYSIS OF EFFICIENCY OF APPLICATION OF DIFFERENT APPROACHES TO DESTRUCTION OF INFORMATION ON MAGNETIC MEDIA

The introduction and active use of information transmission and storage systems in the Ministry of Defense (MoD) of Ukraine form the need to develop ways of guaranteed removal of data from media after their use or long-term storage. Such a task is an essential component of the functioning of any information security system. The article analyzes the problems of guaranteed destruction of information on magnetic media. An overview of approaches to the guaranteed destruction of information on magnetic media of different types is presented, and partial estimates of the effectiveness of their application are given by some generally accepted indicators of performance evaluation. The article also describes the classification of methods of destruction of information depending on the influence on its medium. The results of the analysis revealed the main problems of application of software methods and methods of demagnetization of the information carrier. The issue of guaranteed destruction of information from modern SSD devices, which are actively used in the formation of new systems of information accumulation and processing, became particularly relevant in the article. In today's conditions of development of the Armed Forces of Ukraine, methods of mechanical and thermal destruction are more commonly used today. In the medium term, the vector of the use of information elimination methods will change towards the methods of physical impact by the pulsed magnetic field and the software methods that allow to store the information storage device, but this today requires specialists to develop new ways of protecting information in order to avoid its leakage.

Features of the Low-Temperature Heat Capacity of Er3 –xTmxAl5O12 Garnet Single Crystals

In this paper, we present the results of studies of the heat capacity of single-crystal garnets Er3 ‒ xTmxAl5O12 (x = 0, 1, 2, 3) in magnetic fields of up to 9 T and in the temperature range 1.9–220 K. The temperature dependences of the heat capacity are approximated using the sum of the contributions of Schottky anomalies associated with magnetic Er3+ and Tm3+ ions and the Debye and Einstein lattice contributions. Entropy and magnetic entropy are calculated using the heat capacity data. With an increase in the magnetic field, entropy is shown to decrease. This indicates the possibility of using the studied garnets in the adiabatic demagnetization method.

Magnetic Testing of Stressed State of Hydrotested Gas-Separator Wall

The stressed state of a hydrotested gas separator has been studied by magnetoelastic demagnetization. Correlation dependences are obtained between the level of magnetoelastic demagnetization of a complex-loaded gas-separator wall and the magnitude of hoop, meridian, and equivalent stresses it experiences. The magnetoelastic demagnetization of a residually magnetized test-object wall, loaded with internal pressure, was estimated from the change in the strength of its magnetic stray field measured along the normal (Hn) and tangent (Hτ) to the surface. It has been established that the growth of mechanical stresses in the separator wall to half the value of the yield strength of steel it is made of causes a noticeable irreversible decrease in the normal (Hn) and tangential (Hτ) components of the strength of its magnetic stray field in the residually magnetized area. It is shown that the method of magnetoelastic demagnetization has the highest sensitivity to mechanical stresses and is easiest to implement and most prompt compared with coercimetry and tensometry.

Multi-Field Coupling Analysis and Demagnetization Experiment of Permanent Magnet Retarder for Heavy Vehicles (MAY 2018)

A new permanent magnet retarder (PMR), which based on the principle of eddy-current braking, is proposed as an auxiliary braking apparatus for heavy vehicles. Its braking torque can be stepless adjusted by the adjustment mechanism. A multi-physics field coupling model of the retarder was established, which includes electromagnetic field, thermal field, and fluid field. The distributions of the three fields were calculated using the finite-element method. To predict the demagnetization of the permanent magnet, a new analysis method of the permanent magnet irreversible demagnetization is proposed, which uses the dynamic air-gap flux density simulated under various temperature B-H curves and the relationship between the braking torque, as well as the square of air-gap flux density. The braking torque and temperature rise of the PMR were tested on the bench. The bench test results show that the braking torque calculated by the multi-physics coupling method agrees better with the experimental data, and the high-temperature irreversible demagnetizations of the permanent magnet occurred by the enormous heat generated during continuous braking. The vehicle test results show that the braking distance can be shortened by 34% after using the PMR, and the braking deceleration is increased by 1.05 m/s 2 . The proposed PMR can meet the requirements of auxiliary braking for heavy vehicles.

Simulation of Reversal Magnetization Processes Caused by Difficulty of Detachment of Domain Wall in Uniaxial Highly Anisotropic Ferromagnets

Processes of reversal magnetization in Sm(Co, Cu, Fe, Zr) 7.4-type alloys are simulated on the basis of the assumption that this process is determined by difficulty of detachment of domain walls from the places of their fixation. The behavior of the material is studied under magnetization after different methods of demagnetization, i.e., cyclic and thermal ones, and by a negative field. The obtained distributions of the fixing fields are used to plot minor loops for actual magnets. The computed and experimental data are compared.

An Improved Analysis Method of Irreversible Demagnetization for a Single-Phase Line-Start Permanent Magnet Motor

This paper presents an effective analysis method of irreversible demagnetization for a line-start permanent magnet (PM) motor considering the magnetic field produced by secondary conductor bars. The magnetic field produced by the secondary conductor bars opposes the variation of the magnetic field caused by the primary part, and these result in the reduced magnetic field acting on the PM. By using finite element analysis in the transient magnetic field, currents in the primary and secondary conductors are estimated and used for demagnetization analysis of the magneto-static field. Therefore, conditions closer to actual situations can be achieved. Both the general demagnetization analysis method, using only primary currents, and presented analysis method are compared and the results are verified by experiments. General demagnetization analysis leads to over-estimation of the magnetic field acting on the PM, and results in excessive PM usage.