Magnetic Repulsive Force Research Articles

Magnetic and Thermal Properties of HTS Bulk Magnet in the Pulsed-Field Magnetizing Process

In order to enhance the field-trapping ability of high Tc superconducting melt-textured bulk materials which act as quasi-permanent magnets when they capture the external magnetic fields, it is important to enhance the mechanical toughness of the materials to stand the stress induced by the magnetic repulsive force and thermal expansion. We adopted a dense Dy123-based bulk material with reduced void concentration in the experiment. Since the heat generations due to the flux motions in the samples results in the degradation of Jc, the time evolutions of the trapped magnetic fields and the temperature rises during and after the pulsed-field magnetizing processes were precisely measured at the same time to evaluate the penetrating flux motions and the heat generations in the sample. A single and couple of the magnetic pulsed fields with various intensities were successively applied to the sample at 30 K. The single magnetic field application exhibited a peak effect in the trapped-field behavior and tended to decline due to the heat generation. In the iterative pulsed-field application, the behaviors of the trapped fields and the temperature changes were found to be inverse between the first and the second pulsed-field applications. This implies that the flux penetration behavior into the sample magnet at the second field application is strongly restricted by the presence of former trapped fields which were formed by the first field applications.

Label-Free Cell Separation Using a Tunable Magnetophoretic Repulsion Force

This paper describes a new label-free cell separation method using a magnetic repulsion force resulting from the magnetic susceptibility difference between cells and a paramagnetic buffer solution in a microchannel. The difference in the magnetic forces acting on different-sized cells is enhanced by adjusting the magnetic susceptibility of the surrounding medium, which depends on the concentration of paramagnetic salts, such as biocompatible gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA), dissolved therein. As a proof-of-concept demonstration, Gd-DTPA solutions at concentrations of 0-80 mM were applied to separate U937 cells from red blood cells (RBCs) and to distinguish two different-sized polystyrene (PS) beads (8 and 10 μm in diameter). By increasing the Gd-DTPA concentration from 0 to 40 mM, the separation resolution of PS beads was increased from 0.08 to 0.91. Additionally, we successfully achieved label-free separation of U937 cells from RBCs with >90% purity and 1 × 10(5) cells/h throughput using a 40 mM Gd-DTPA solution.

Analysis and design of a moving-magnet type linear actuator with repulsive magnetic forces

The paper describes a newly developed miniature moving-magnet type linear actuator with proportional action that uses repulsive magnetic forces. Out of four possible structures, two with mobile magnets and two with fixed ones, the most simple and cheap prototype was chosen, offering good possibilities to obtain a miniature structure. A comparative numerical analysis for two types of mobile element justifies the adopted constructive solution. A laboratory prototype was analyzed numerically and experimentally in view of a possible optimization, the experimental and numerical results being in good agreement. Finally a prototype actuator was built and tested.

Simple Electro-Mechanical Model of Magnetic Spring Realized from FeNdB Permanent Magnets

Abstract Magnetic spring utilizing the repulsive force of two permanent magnets is a new device with application in special textile machines. In order to get reliable rules for its design, the effect of geometrical parameters, magnetic properties, material deviations and mechanical inaccuracies should be known, first of all. The paper presents very simple model of permanent magnets based on surface bounded currents and gives information from detailed measurement of ring shape magnet both of the magnetic field and repulsive force. At present time the magnetic field measurement was performed only in a plane parallel to the spring plane. Nevertheless, the agreement with theory is good and the experimental errors can be estimated and reduced by the method of trials and errors. The value of magnetic flux density agrees with the producer data and its deviation can reach up to 10% along the concentric circle. Also, the direct measurement of repulsive force agrees well with both the simple theory and two-dimensional FEM. Ring magnet with outer diameter of 25 mm exhibits magnetic flux density of 1.15 T on its surface and a repulsive force of about 70 N in close contact between magnets. The dynamic magnet aging was studied, too. The changes in both the magnetic field and repulsive force were negligible after 30 million cycles. After finishing the experiments, the method and all the results can make very efficient and simple design of magnetic spring.

Electro-magnetic collapse of thick-walled cylinders to investigate spontaneous shear localization

We present an electro-magnetic (EM) setup in order to collapse thick-walled cylinders, for the investigation of spontaneous formation of multiple adiabatic shear bands. The EM setup is based on a pulsed current generator using a capacitor bank system. The cylindrical specimen is part of an assembly of coaxial cylinders, where the inner and outer cylinders, each attached to an opposite pole, are short-circuited. Upon capacitor discharge, a high current flows through the cylinders, in opposite directions, creating repulsive magnetic forces between them. The outer cylinder is driven outwards and the inner cylinder is driven inwards – in a collapsing manner. This work presents the design procedure of the specimens’ geometry using numerical simulations, and some preliminary experimental results for SS304L steel specimens. The spatial distribution of the multiple adiabatic shear bands in these specimens is in good agreement with that reported in the literature for explosively driven experiments with the same material. Our numerical simulations of the collapsing cylinder show good agreement with the experimental results for both global behavior and shear band distribution.

Innovative Electromagnetic Actuator Applied for High-Frequency Reciprocal Translation

A novel magnetically levitated linear actuator, mainly consisting of a Halbach magnetized moving-magnet armature, a cylindrical frame, a rod, and electromagnetic poles, is presented and analyzed for linear compressors applications. The Halbach magnetized armature naturally generates a periodically distributed magnetic field, which is interacted with that induced by the electromagnetic poles. Therefore, an axially reciprocating thrust force is induced that is inherently suitable for high-frequency drive for linear compressors. A lateral magnetic repulsive force, due to the eddy current induced at the cylindrical frame, to exert upon the rod is generated as long as the rod is deviated in the radial direction. Once the position of the rod is laterally deviated from the central position, the rod is automatically brought back by this magnetic repulsive force. The magnetic field distributions, axial thrust force, and lateral magnetic repulsive force are numerically obtained by governing equations analysis under the cylindrical coordinate. The finite element method, by the commercial software ANSOFT Maxwell with Transient Solver (Ansoft Corporation, Pittsburgh, Pennsylvania, USA), is employed to be compared with and validate the solutions obtained by the governing equations analysis. It is shown that the governing equations analysis extremely agrees with the results by the finite element method. At last, the efficacy of the proposed magnetically levitated linear actuator is examined and verified by intensive computer simulations and experiments.

Initial in vivo evaluation of the newly developed axial flow turbo pump with hydrodynamic bearings

An implantable, compact rotary blood pump has been newly developed using an axial flow turbo pump with hydrodynamic bearings. The rotating impeller, which is hydrodynamically levitated with the assistance of repulsive magnetic force, has no contact with the inner surface of the pump. To evaluate the hemodynamic performance and biocompatibility, the pump was installed into four calves for up to 90 days. The pump was installed in the left heart bypass fashion, and placed paracorporeally in the first two calves and in the thoracic cavity in the other two calves. All calves received anticoagulation and antiaggregation therapy during the study. Aortic pressure, heart rate and pump-operating parameters were continuously measured. Hematologic and biochemical tests to evaluate anemia, hepato-renal function and the extent of hemolysis were performed on schedule. Each calf was killed at the termination of the experiments, and pathological analysis for the biocompatibility of the pump system was performed, including the thrombi in the device, emboli in the systemic organs and signs of infection. The pump stably produced a flow of 5 l/min. Each calf was supported for 78, 50, 90 and 90 days, respectively, with no incidence of hemorrhage, organ failure or significant hemolysis. No thrombus formation or mechanical wearing was observed inside the pump. There was no evidence of heat injury around the pump. Device-related infections were observed, but the severity of infection was mild in the implant case compared to the paracorporeal case. The pump demonstrated acceptable hemodynamic performance and biocompatibility in the initial in vivo testing.

Design Concepts and Principle of Operation of the HeartWare Ventricular Assist System

Implantable left ventricular assist devices provide circulatory support for patients at risk of death from refractory, end-stage heart failure. Rotary blood pumps have been designed for increased reliability and smaller size for use in a broader population of patients than the first-generation pulsatile devices. The design concepts and principle of operation of the HeartWare System are discussed. The HeartWare Ventricular Assist System (HVAD) is a small centrifugal flow pump with a displacement volume of 50 ml and an output capacity of 10 L/min. A unique wide-blade impeller is suspended by hybrid passive magnets and hydrodynamic forces. An integrated inflow cannula is inserted into the left ventricle and is held in position by an adjustable sewing ring; the pump is positioned in the pericardial space. The 10-mm outflow graft is anastomosed to the ascending aorta. External system components include the microprocessor-based controller, a monitor, lithium-ion battery packs, alternating current and direct current power adapters, and a battery charger. Physiologic control algorithms are incorporated for safe operation. Preclinical life cycle tests have shown the HVAD to be highly reliable. This system design offers reliability, portability, and ease of use for ambulatory patients.

Design and analysis of magnetically-drive actuator applied for linear compressor

A novel Magnetically Levitated Linear Actuator (MLLA), mainly consisting of a Halbach magnetized moving-magnet armature, a cylindrical frame, a rod and electromagnetic (EM) poles, is presented and analyzed for linear compressors applications. The Halbach magnetized armature naturally generates a periodically distributed magnetic field which is interacted with that induced by the EM poles. Therefore, an axially reciprocating thrust force is induced that is inherently suitable for high frequency drive for linear compressors. A lateral magnetic repulsive force, due to the eddy current induced at the cylindrical frame, to exert upon the rod is generated as long as the rod is deviated in the radial direction. Once the position of the rod is laterally deviated from the central position, the rod is automatically brought back by this magnetic repulsive force. The magnetic field distributions, axial thrust force and lateral magnetic repulsive force are numerically obtained by Governing Equations Analysis (GEA) under cylindrical coordinate. The Finite Element Method (FEM), by the commercial software ANSOFT Maxwell with Transient Solver, is employed to be compared with and validate the solutions obtained by GEA. It is shown that the GEA is extremely agreed with the results by FEM. At last, the efficacy of the proposed MLLA is examined and verified by intensive computer simulations and experiments.

Vibration Suppression of the Rotating Shaft using the Axial Control of the Repulsive Magnetic Bearing

A repulsive magnetic bearing supports a rotating shaft without contact by utilizing a magnetic repulsive force between the magnets. However, because of the nonlinear characteristic of the magnetic repulsive force, the vibration during passage through the critical speed may increase. This paper investigates a vibration suppression method of the rotating shaft supported by the repulsive magnetic bearing. A vibration suppression method by controlling the axial displacement of the repulsive magnetic bearing is proposed. Its axial displacement control generates the changes of both the linear and the nonlinear coefficients of stiffness. The influence of the parameters of the axial displacement control are investigated, and these results are validated experimentally.

Study of an ultrafine w-EDM technique

A precision ultrafine w-EDM (wire electrical discharge machining) technique specifically for machining intricate parts and structures is developed in this paper. A thumb-sized and versatile w-EDM device equipped with a complete control system for wire tension (ultrafine tungsten wire of 13 µm diameter) is designed and employed for the study of ultrafine w-EDM. The tension of the wire electrode is controlled by magnetic repulsive force to steady the wire during machining. Ultrafine wire cutting can be conducted in vertical-, horizontal- or slantwise-wire arrangements. Via some experiments, optimal machining conditions including discharge capacitance, feed rate, wire tension and the appropriate design for the w-EDM device are obtained. Two miniature samples including a micro of Taipei's landmark 101 building and a micro relay are fabricated and the feasibility of the proposed approach is verified. It is confirmed that the ultrafine w-EDM technique using an ultrafine tungsten wire of 13 µm was realized successfully.

Design and Characterization of a Magnetically Driven Valveless Micropump for Drug Delivery

Micropump, an actuation source to transfer the fluid from reservoir to the target place with accuracy and reliability, plays an important role in microfluidic devices. A broad range of micropump applications in biomedical fields are found in the fluid fine regulation and precise control systems for implantable drug delivery, chemical and biological detection, as well as blood transport in cardiology system. A polydimethylsiloxane (PDMS) magnetic composite membrane based on microfabrication with dimensions of 6 mm and 65 μm in diameter and thickness respectively, is employed to actuate a proposed micropump. In micro pumping operation, the fluid flow effects on the actuation and dynamic response of an oscillating membrane are curial to the design of the micropump. Therefore, the resonant frequency of this micro device is estimated considering the added mass and fluid damping to understand the behaviors of the valveless micropump. In this study, the membrane actuation is implemented by a miniaturized electromagnet, which provides an external time-varying magnetic field. The magnetic force on the membrane is proportional to the gradient of the magnetic field and the magnetization of the micro particles embedded in the membrane. The alternating attractive and repulsive magnetic forces on this composite membrane are computed by Finite Element Analysis (FEA). The basic design issues of the electromagnetic actuator involving air gaps, input current signals, and distribution of magnetic flux in the magnetic circuit are presented. Moreover, the magnetic-structure coupling analysis is conducted to determine the maximum deformation and stresses on the membrane, which result from the action of these magnetic forces. Finally, frequency-dependent flow rate of a dual-chamber configuration micropump has been studied. The pumping rate increases almost linearly with the excitation frequency at low ranges and there exists resonant frequencies at which the flow rate will reach a maximum value. After the flow rate peaks, the pumping rate decreases sharply along with the actuating frequencies. The maximum flow rate for the dual-chamber remains at 27.73μl/min under 0.4 A input current with an excitation frequency of 3 Hz. For comparison, a single-chamber micropump reaches a maximum flow rate of 19.61μl/min with a resonant frequency of 4.36 Hz under the same condition.

Design of a Halbach Magnet Array Based on Optimization Techniques

We have designed a Halbach magnet array by using a numerical optimization method based on finite-element analysis. The magnetization direction of each element is defined as the design variable. The optimal magnet arrays composed of two and three linear magnet layers can then be investigated to increase the attractive, repulsive, and tangential magnetic forces between magnet layers. We have applied a magnet array maximizing the tangential force to a torsional spring composed of two- and three-magnet rings. The two-dimensional finite-element analysis incorporates optimization techniques such as the sequential linear programming and the adjoint variable method.

Performance of a guideway seismic isolator with magnetic springs for precision machinery

AbstractThis paper proposes the use of the nonlinear restoring force in an isolation system to improve the performance of a seismic isolator. Nonlinear magnetic springs applied to guideway sliding isolators (GSI) that protect precision machinery against seismic motion were studied. The magnetic springs use a non‐contact magnetic repulsion force to achieve a nonlinear property. A numerical simulation model of the GSI system using step‐by‐step integration in the time domain was developed. A full‐scale shaking table test was performed to verify the accuracy of the numerical model. Simulation and experimental results show that the GSI system with magnetic springs has good performance when subjected to floor vibrations during earthquakes. A parametric analysis of the magnetic springs in the GSI system under seismic motion was theoretically investigated. It was found that sufficient magnetic forces can diminish the system relative displacements. Copyright © 2008 John Wiley & Sons, Ltd.

Initial condition influence on coronal mass ejection propagation

In the melon‐seed‐overpressure‐expansion (MSOE) model described by Siscoe et al. (2006) for the acceleration of coronal mass ejections (CMEs), magnetic repulsion force plays a central role. MSOE is a combination of Pneuman's (1984) melon seed concept with an overpressure expansion analytically formulated by Siscoe et al. (2006). The MSOE model creates a reduced formalism to describe CME acceleration and is highly advantageous for comparative studies. As originally presented, the MSOE model has the drawback of being able to produce only fast CMEs. For the work presented in this paper, we compare the acceleration of a 2.5‐D magnetohydrodynamics (MHD)‐modeled CME with that of a version of the MSOE model. On the basis of the results of the MHD simulations, we divide the acceleration of a CME into two phases: (1) a tethered phase before detachment (when the CME is tethered by external closed loops) and (2) a repulsion phase after detachment (when the tethering force that binds the CME is much smaller than outward magnetic repulsion force). We find that during the repulsion phase, the acceleration can be described well by the standard MSOE model. However, during the tethered phase, the CME acceleration is much slower than MSOE predictions. We therefore refine the MSOE model to include tethering and can account for both fast and slow CMEs with the final CME speed controlled by the CME detachment height.

Development and Evaluation of an Active Magnetic Guide for Microsystems With an Integrated Air Gap Measurement System

An active magnetic levitation system based on repulsive magnetic forces was developed as a guide for a linear hybrid microstep motor. With this levitation system, the vertical force, which is typically an order of magnitude greater than the driving force, can be compensated. A capacitive measurement system provides measurement data to maintaining a constant air gap. This paper presents the design, fabrication, and first measurement results of the magnetic guide and the air gap measurement sensor

Experiments on the reflection of cold atoms from magnetic thin films

We report the results from a series of experiments in which ferromagnetic thin films were used as atom mirrors for laser-cooled rubidium atoms released from a magneto-optical trap. The thin films were made of cobalt and lanthanum calcium manganite (LCMO) with thicknesses between 20 and 300 nm. The magnetic domains in these thin films have a periodic structure where the spatial period is of the order of the thickness of the film, and the field decays exponentially above the film over a length scale comparable to the domain size. Thus, the neutral atoms reflect off these films from distances comparable to the thickness of the film, resulting in modification of the reflectivity due to the competition between the repulsive magnetic force and the attractive short-range forces such as van der Waals and Casimir forces. The smoothness of the atom mirror is also modified due to the proximity of the magnetic domains. The reflectivity is sensitive to the domain structure and size, which can be modified in LCMO by applying a modest external magnetic field. In this paper, we discuss the evaluation of the thin films as magnetic mirrors for atom optics, and the measurement of the van der Waals force with an accuracy of about 15%, using cobalt thin films. We also discuss some preliminary results on the temperature-dependent reflectivity for atoms near the ferromagnetic transition at 250 K in the LCMO film, and on the domain dynamics and relaxation.

Magnetic Repulsive Forces on ArmatureContacts

Transition to arcing contact in solid-armature railguns has been linked to several mechanisms. Recent work suggests magnetic blowoff forces arising from perimeter erosion as a possible significant mechanism. Three-dimensional finite-element (FE) models were constructed to analyze the repulsive contact forces resulting from perimeter erosion. Results show that magnetic blowoff occurs only when there is a loss of more than 98% of the contact area. Such gross perimeter erosion is unlikely and is not found in recovered armatures. Magnetic liftoff from perimeter erosion does not appear to be a causative mechanism in armature transition. This computational study also provided a platform for testing two FE codes, which showed very good agreement overall

Magnetic Spinner

A science toy sometimes called the “magnetic spinner” is an interesting class demonstration to illustrate the principles of magnetic levitation. It can also be used to demonstrate Faraday's law and a horizontally suspended physical pendulum. The levitated part contains two circular magnets encased in a plastic housing. Each magnet stays above two triangular magnets fixed to the base. The magnetic repulsive force experienced by the circular magnets is independent of their orientation; therefore, the holder of these magnets can be rotated without affecting its stability. The holder with the circular magnets can be oscillated up and down as a horizontally suspended physical pendulum.

Magnetic Levitation Assisted Guide for a Linear Micro-Actuator

In linear micro-actuators based on the electromagnetic driving principle, attractive vertical forces are generated between stator and traveler in addition to the drive forces. These vertical forces reduce the resulting driving force of the motor depending on the quality of the applied guide system. Thus, the development of an adequate guide system with a very small friction is required to guarantee an efficient operation mode. This paper describes the development of a guide system based on repulsive magnetic forces to partially compensate the vertical forces of a linear hybrid step micromotor