Permanent Magnet Rings Research Articles

Research on the orientation structure of permanent ferrite multi-polar magnet ring

Research on the orientation structure of permanent ferrite multi-polar magnet ring

A bistable vibration isolator with nonlinear electromagnetic shunt damping

Abstract This paper presents a bistable vibration isolator (BVI) with several ring permanent magnets (PMs) and utilizes nonlinear electromagnetic shunt damping (N-EMSD) to improve the vibration isolation performance of the BVI. The theoretical model of N-EMSD is established. The harmonic balance method (HBM) is employed to derive the transmissibility of the BVI with N-EMSD. The analytical, numerical and experimental efforts are performed to investigate the vibration isolation performance of the BVI with N-EMSD. The results demonstrate that when the BVI is in the interwell oscillation, two peaks appear in the transmissibility curve and the transmissibility could be smaller than 1 between the two peaks. With the increase of the negative resistance, the motion of the BVI changes from the aperiodic/chaotic interwell oscillation to intrawell oscillation, resulting in the increase of the isolation band and the improved vibration isolation performance. The effects of the nonlinear electromagnetic coupling coefficient and the negative resistance are also investigated. The BVI with N-EMSD provides a feasible approach to study the vibration isolation characteristic of bistable structures.

Calculation and Measurement of the Magnetic Field of Nd2Fe14B Magnets for High-Temperature Superconducting Magnetic Bearing Rotor

The external magnetic flux density and distribution of the permanent magnet (PM) rotor of the high-temperature superconducting (HTS) magnetic bearing directly affect the load-carrying properties and stability of the HTS magnetic bearing. In order to facilitate the design of the PM rotor that meets the application requirements, a finite element analysis (FEA) method to calculate the magnetic flux density and distribution of PM rings and PM rotor would be used. A magnetic field measurement system was built as well. By comparing the results of calculation and measurement, the validity of the magnetic field calculation method is verified. And the calculation results are promoted after correcting the calculation parameters of the magnetic ring. Therefore, the correctness and accuracy of the calculation method are verified by experimental measurement. The magnetic field measurement system can be used to measure and select the magnetic rings with uniform and consistent magnetic field to improve the stability of the HTS magnetic bearing. And the performance of the Nd2Fe14B magnets N52 at liquid nitrogen temperature (77 K) was measured, which has been increased by about 9% relative to magnetic field at room temperature (295 K).

Evaluation of loss characteristics of superconducting magnetic bearings for LiteBIRD satellite by three-dimensional finite element method analysis

The polarization modulator of LiteBIRD satellite is required to be used by continuously rotating the half-wave retarder under a low temperature environment of about 10 K. Then, it becomes an important issue to reduce heat generation due to rotation loss. Therefore, a rotation mechanism in a cryogenic environment by a superconducting magnetic bearing (SMB) using the pinning effect of the bulk superconductor has been studied. In SMB, because of the pinning effect of superconductor, it is possible to rotate the half-wave retarder with stably floating, and it is possible to avoid frictional heat due to contact. The half-wave retarder is incorporated inside the rotating part of the superconducting magnetic bearing composed of the permanent magnet ring and the iron yoke. At this time, since the permanent magnet ring divides the parallel magnetized permanent magnets into pieces, a gap is formed at the joint of the permanent magnets. For this reason, the magnetic field distribution generated by the permanent magnet ring is not uniform. Although SMB can reduce friction as compared to mechanical bearings, the magnetic properties of the bulk superconductor change due to the magnetic field fluctuation caused by such ununiformity of the magnetic field, resulting in energy loss. In this study, heat generation in bulk superconductor in SMB is evaluated by three-dimensional finite element method. First, using JMAG Designer 17.0, the magnetic field distribution created by the rotor side is obtained by static magnetic field analysis. Next, using the COMSOL Multiphysics 5.3a, by applying the magnetic field distribution created by the rotor side obtained above and rotate the magnetic field, the loss generated in the bulk superconductor is investigated. The resulting loss value satisfied the required value.

Effect of the position of the external magnetic field applied to a glow discharge plasma on the coherent forward scattering spectra in the Faraday configuration

The coherent forward scattering (CFS) spectra of the Ar I 842.5 nm and O I 844.6 nm lines in a radio-frequency (RF) plasma were measured. The CFS spectrometer used was equipped with a movable permanent ring magnet in the Faraday configuration and a diode laser source. The CFS signal was mainly generated near the maximum external magnetic field applied. When the ring magnet was moved toward the RF-powered electrode of the glow discharge tube, the analytical curves of the excited argon atoms in the lower state of the Ar I 842.5 nm transition became nonlinear because these atoms were depleted under the partial Ar pressure (0.04 Torr (5.3 Pa) or less). When the ring magnet was moved toward the grounded electrode, no depletion of the excited Ar atoms was observed, resulting in linear analytical curves. Similar depletion of the excited atoms in the lower state of the O I 844.6 nm transition was also observed at the RF-powered electrode.

The design of negative stiffness spring for precision vibration isolation using axially magnetized permanent magnet rings

A negative stiffness element is always employed to generate high-static–low-dynamic stiffness characteristic of the vibration isolator, reduce the resonance frequency of the isolator, and improve the vibration isolation performance under low and ultra-low frequency excitation. In this paper, a new compact negative stiffness permanent magnetic spring (NSPMS) that is composed of two axial-magnetized permanent magnetic rings is proposed. An analytical expression of magnetic negative stiffness of the NSPMS is deduced by using the Coulombian model. After analyzing the effect of air-gap width, air-gap position, height difference between the inner ring and outer ring on the negative stiffness characteristic, a design procedure is proposed to realize the negative stiffness characteristic with a global minimum linear component and uniformity stiffness near the equilibrium position. Finally, an experimental prototype is developed to validate the effectiveness of the NSPMS. The experimental results show that combining a vibration isolator with the NSPMS in parallel can lower the natural frequency and improve the isolation performance of the isolator.

Isotropic Alloys of the Sm – Co System for Ring Magnets with Radial Magnetization

Methodology of creation of ring permanent magnets with radial magnetization from an isotropic alloy of the Sm – Co system with induction coercivity no lower than 280 kA/m is presented. Special attention is devoted to the temperature stability of the magnetic parameters and to the strength characteristics of the alloys studied. A method for magnetization of isotropic ring magnets from Sm – Co-base magnets in radial direction is suggested. Ring permanent magnets with radial magnetization are tested in actual magnetic systems. The characteristics of textured and isotropic magnets are compared.

Low-frequency band gaps in a metamaterial rod by negative-stiffness mechanisms: Design and experimental validation

A metamaterial rod with resonators containing negative-stiffness (NS) mechanisms is proposed for generating very low-frequency bandgaps. The underlying principle employs the NS mechanism (a pair of mutual repelling permanent magnet rings) to partially or totally neutralize the stiffness of the positive-stiffness element (two coil springs) of the resonator and thus to achieve an ultralow, even zero, stiffness, which enables a significant shift of the bandgap from a high frequency to a low one. Experiments on the restoring force feature of the resonator and the bandgap of the metamaterial rod are carried out, which provide sufficient evidence to validate the proposed concept for substantially lowering bandgaps in locally resonant metamaterials. This study opens a potential path to manipulate elastic waves within a very low-frequency range.

Efficiency enhancement of a point wave energy converter with a magnetic bistable mechanism

In this study, a compact magnetic bistable mechanism is proposed to enhance the efficiency of a point wave energy converter (WEC) with a linear damper like Power Take-off (PTO) system. The magnetic bistable mechanism mainly consists of two coaxial permanent magnet rings with the same magnetic field direction. The dynamic model in the time domain for the nonlinear point absorber is established by using the state space method to replace the convolution term. The wave energy capture characteristics are analyzed in regular and irregular waves. The numerical results show that the magnetic bistable mechanism can shift the frequency bandwidth of the point wave absorber to the lower frequency which covers the realistic wave excitation frequencies in regular wave. The efficiency for the bistable WEC with large inter-well oscillations can be enhanced by about two times comparing with that of a classical linear WEC in irregular waves.

Homogeneous electrogenerated chemiluminescence immunoassay for the detection of biomarkers by magnetic preconcentration on a magnetic electrode.

A homogeneous electrogenerated chemiluminescence (ECL) immunoassay for highly sensitive quantification of specific biomarkers based on immunomagnetic beads and homogeneous detection on a magnetic electrode was developed, for the first time. The magnetic electrode is made of a glassy carbon electrode and a series of ring permanent magnets. D-Dimer antigen was taken as a model analyte while biotinylated D-dimer antibody bound on the streptavidin-coated magnetic beads was utilized as a magnetic capture probe and ruthenium complex-labeled D-dimer antibody was employed as an ECL probe. After a fixed amount of magnetic capture probe and the ECL probe was introduced into analyte D-dimer solution, the "sandwich" immunoconjugates on the magnetic beads were formed in tested solution and then magnetically concentrated on the surface of the magnetic electrode. The homogeneous ECL immunoassay for quantification of specific biomarker was directly carried out in the presence of co-reactant tripropylamine. The low detection limit of 1ng/mL in magnetic enrich time of 2min and the good magnetic regeneration for the detection of D-dimer were achieved. The magnetic bead shield ECL emission was extensively discussed. This work demonstrates that the homogeneous (separation-free) ECL immunoassay using magnetic beads and magnetic electrode is a promising approach to quantify the biomarkers with high sensitivity and selectivity and in a short time. This approach can be easily extended to ECL and electrochemical biosensing for other biomarkers. Graphical abstract.

Development of Vibration Isolator With Controllable Stiffness Using Permanent Magnets and Coils

Abstract In this study, a novel vibration isolator is presented. The presented isolator possesses the controllable stiffness and can be employed in vibration isolation at a low-resonance frequency. The controllable stiffness of the isolator is obtained by manipulating the negative stiffness-based current in a system with a positive and a negative stiffness in parallel. By using an electromagnetic device consisting of permanent magnetic rings and coils, the designed isolator shows that the stiffness can be manipulated as needed and the operational stiffness range is large in vibration isolation. We experimentally demonstrate that the modeling of controllable stiffness and the approximation of the negative stiffness expressions are effective for controlling the resonance frequency and the transmissibility of the vibration isolation system, enhancing applications such as warship stealth technology, vehicles suspension system, and active vibration isolator.

Characterization of hydrogen plasma in a permanent ring magnet based helicon plasma source for negative ion source research

HELicon Experiment for Negative ion source (HELEN-I) with a single driver is developed with a focus on the production of negative hydrogen ions. In the Helicon wave heated plasmas, very high plasma densities (1018–1019 m−3) can be attained with electron temperatures as low as ∼1 eV in the downstream region. These conditions favor the production of negative hydrogen ions. In HELEN-I device at IPR, helicon plasma is produced using Hydrogen gas by applying a RF power (PRF) of 800–1000 W at 13.56 MHz frequency. A Nagoya-III antenna is used to excite m = 1 helicon mode in the plasma. A permanent ring magnet creates the required axial magnetic field. The plasma is confined by a multi-cusp field configuration in the expansion chamber. The transition from inductively coupled mode to Helicon mode is observed near PRF ∼ 700 W with plasma density ∼1018 m−3 and electron temperature ∼5 eV in the driver and ∼1 eV in the expansion volume. Negative hydrogen ion density, averaged over the line of sight, is measured in the expansion chamber by employing an optical emission spectroscopy diagnostic technique using Hα/Hβ ratio and a laser photodetachment based cavity ring down spectroscopic diagnostic technique. The measured value of negative hydrogen ion density is in the order of 1016 m−3 at 6 m Torr pressure and does not vary significantly with power, pressure and downstream axial magnetic field variation in the helicon mode. The negative ion density measurements are compared with theoretically estimated values calculated using a particle balance method considering different reaction rates responsible for negative hydrogen ion creation and destruction. It is to be noted that, at present, cesium is not injected in the plasma discharge to enhance H− ion density.

The effect of adding an axial magnetic field on the expansion of a laser-produced plasma

We use a pulsed ultraviolet laser to ablate a copper target in order to study the effects of adding a permanent and axial magnetic field on the plasma plume expansion. The laser pulse duration is 20 ns, its energy is 150 mJ, and it is focused on a surface of about 1 mm2. The target is inserted at the center of a ring permanent neodymium magnet as we compare data taken with and without the magnetic field using a Langmuir probe that is installed at 2.5 cm from the target but is capable of moving radially. The magnetic field, B, affects the plasma plume by reducing its expansion and by increasing the plasma temperature significantly. We report, and for the first time, the measurement of the average axial as well as the radial electric fields and show that both are enhanced in the presence of a magnetic field. This yields a strong increase in the plasma current and thus that of ohmic heating, which could help in explaining the temperature increase recorded by different groups when a magnetic field is added to the plasma plume expansion.We use a pulsed ultraviolet laser to ablate a copper target in order to study the effects of adding a permanent and axial magnetic field on the plasma plume expansion. The laser pulse duration is 20 ns, its energy is 150 mJ, and it is focused on a surface of about 1 mm2. The target is inserted at the center of a ring permanent neodymium magnet as we compare data taken with and without the magnetic field using a Langmuir probe that is installed at 2.5 cm from the target but is capable of moving radially. The magnetic field, B, affects the plasma plume by reducing its expansion and by increasing the plasma temperature significantly. We report, and for the first time, the measurement of the average axial as well as the radial electric fields and show that both are enhanced in the presence of a magnetic field. This yields a strong increase in the plasma current and thus that of ohmic heating, which could help in explaining the temperature increase recorded by different groups when a magnetic field is added to...

Strength analytical solution to ultra-high-speed permanent magnet rotor considering temperature gradient and segmental permanent magnet effect

Ultra-high-speed permanent magnet synchronous motors usually adopt the rotor in which a sleeve is interference fitted onto a ring permanent magnet or segmental permanent magnets. The rotors are alw...

Enhanced Bandwidth Nonlinear Resonance Electromagnetic Human Motion Energy Harvester Using Magnetic Springs and Ferrofluid

An enhanced bandwidth nonlinear resonant electromagnetic energy harvester has been designed to harness low frequency energy from basic human motions. The inertial mass of the proposed harvester is formed by four stacked ring permanent magnets (PMs), which is suspended axially by two magnetic springs and circumferentially by ferrofluid within a carbon fiber tube. The magnetic springs are made up of two button PMs adhered, respectively, to the end cap at each end of the carbon fiber tube to provide varying repulsive forces to the PM stack, resulting in enhanced resonance frequency band and higher efficiency in energy harvesting. The ferrofluid that self-assembles around the edges of the PM stack acts as its bearing system to minimize frictional losses during its movement. Copper wire is wrapped outside the tube to form the armature winding. The stiffness characteristic of the magnetic springs and the optimum equilibrium position and number of windings have been determined by finite element method analysis. As a proof of concept, a portable prototype of the proposed energy harvester that weighs 110 g and with a volume of only 37.7 cm $^3$ is fabricated. A series of experiments is carried out and the results show that the frequency band of the harvester becomes wider as the external vibration intensity increases. In addition, the effectiveness of ferrofluid in reducing friction is demonstrated under walking and running conditions. Without ferrofluid, the maximum average outputs are 10.15 and 32.53 mW, respectively, for walking and running. With ferrofluid, the maximum outputs are 17.72 and 54.61 mW, representing an increase of $74.58\%$ and $67.88\%$ , respectively. Furthermore, the prototype exhibits an average power density of 1.45 mW/cm $^3$ during running motions, which compares favorably with existing harvesters used in low power wearable devices.

Dynamics and performance evaluation of a novel tristable hybrid energy harvester for ultra-low level vibration resources

To improve the efficiency of energy harvesting from external ultra-low level vibration resources, this article presents a novel tristable hybrid vibration energy harvester using geometric nonlinearity technique to tuning the resonant frequency and broadening the bandwidth. Based on a simple snap-through spring-mass system, it is composed of a piezoelectric ceramics, two ring permanent magnets and a central inertial mass. The device was designed as harvesting energy from low and ultra-low level vibration resources by exploring structural benefits and nonlinear characteristics. The governing electromechanical coupling equations of motion are derived, and a transformation is performed to decouple the equations. The presented device has different nonlinear stiffness properties of the hardening spring effect, softening spring effect and hardening-softening spring effect, which are ideal for the system to harvest broadband energy and suitable for energy harvesting for changing excitation. Compared with monostable and bistable energy harvesters, the tristable energy harvesting has a wider bandwidth for resonance than the bistable or monostable one to enhance the energy harvesting performance over a broadband ultra-low level frequency region. For ultra-low level stochastic fluctuation, results show that the tristable characteristic can lead to a large response and give out a high harvested power.

Comparative analysis and experimental evaluation of single slope solar still augmented with permanent magnets and conventional solar still

Experimental and theoretical evaluation of conventional solar still (CSS) and CSS augmented with permanent ferrite ring magnets (MSS) have been reported. Mathematical model proposed by Kumar & Tiwari has been used for the evaluation of internal heat transfer coefficients, internal efficiency, exergy efficiency, and exergy destruction. The average partial pressure difference between basin water and inner condensing cover surface for MSS has been found to be 77.99% higher than CSS when experiments were carried out for 13 h. The maximum value of evaporative heat transfer coefficient of MSS leads over the CSS by 28.65% at 13:00 h. The distillate yield recorded during the experimentation for MSS is 49.22% higher as compared to CSS. It seems that the magnetization of water has enhanced the overall internal efficiency and exergy efficiency of MSS over CSS by 49.17% and 110.26% respectively. In MSS the presence of permanent magnets has remarkably reduced the exergy destruction in the basin area. Augmentation of magnets with the CSS has significantly enhanced the distillate output of MSS. It has been found that the theoretical results obtained from Kumar & Tiwari numerical model are in good agreement with the experimental results obtained from CSS and MSS.

Dynamic Analysis of the Tubular Linear Actuator With Permanent Magnets

Abstract In this paper a results of a transient analysis of the linear actuator is presented. The linear actuator consist of the three cylindrical unmovable coils surrounded by a soft ferromagnetic case, a runner made from sequence of ferromagnetic and permanent magnet rings. The model of the linear actuator was implemented into two software: the Comsol Multiphysics and the Matlab-Simulink. Both environments are commonly used in simulation analysis, but the first one uses Finite Element Method (FEM) and the second one uses Ordinary Differential Equations (ODE). Moreover, the dynamic model was analysed in Matlab-Simulink software with value of electromagnetic phenomena implemented from Comsol Multiphysics. Comparison was made due to the time needed for calculation, accuracy of the simulation model as well as the as utility for further optimization process.

Technical Aspects of Critical Components for High-Temperature Superconductor Bearings-Based Flywheel Energy Storage System

Flywheel-based energy storage systems are gaining prominence in present-day energy-deficit situation. For energy storage system, the bearings and motor cum generator, for charging and discharging energy to and from the flywheel, form the vital components which have to be given due consideration. The low coefficient of friction of high-temperature superconductor bearings used in flywheel-based energy storage systems decides the energy loss factor. Yttrium Barium copper oxide (YBCO) which is one of the popular high-temperature superconductors is widely being used in high-temperature superconductor bearings. The planar type of bearings can be materialised by building the stator of the bearing with YBCO bulk high-temperature superconductor discs mounted in a circular array and rotor part can be realised by Nd–Fe–B permanent magnet ring which is to be embedded with the flywheel. The levitation force is proportional to the mean magnetization of high-temperature superconductor and the horizontal gradient of the vertical component of the magnetic field density in the superconductor. The magnetization is proportional to the product of critical current density and the grain diameter of the bulk superconductor. The high-temperature superconductor bearings outweigh the magnetic bearings because their passive nature, by virtue, does not require any external active stability balancing devices. The paper discusses of development, fabrication and load testing of prototype planar type of high-temperature superconductor bearings. For charging and discharging energy to and from the flywheel energy storage system, Halbach array-type motor cum generator is a promising candidate. The motor, with an outside rotor design, is a dipole Halbach array, establishing a uniform flux within the stator area. A uniform flux is needed for operating the motor on a superconductor bearing, where slight movement of the stator inside the air gap is inevitable. The salient construction features of the prototype Halbach array motor generator will be discussed.

Effects of difference in inner diameter of adding ring permanent magnets on superconducting magnetic levitation

Effects of difference in inner diameter of adding ring permanent magnets on superconducting magnetic levitation