Radial Magnet Research Articles

Définition d’actionneurs électromagnétiques à débattement limité pour réguler le débit du comburant d’un moteur thermique

The present work is a development of limited motion actuators, dedicated to the combustive regulation of an internal combustion engine. The development is a conception method from an analytical study of several actuators' topologies followed by a geometrical optimization under constraint and a check with a finite element method using Flux2D & 3D™ softwares. The actuators' performances are specified for a small volume with a maximized torque on an angular clearance from 0 to 100 ° at room temperature. Two bipolar permanent magnet actuator topologies are compared: one with axial magnet flux, and the other with radial magnet flux.

Arc Duration and Rotational Frequency of Break Arcs Driven by Radial Magnet Field in a DC42V Resistive Circuit

Break arcs are rotated with the radial magnetic field formed by a magnet embedded in the fixed contact. They are generated in a DC42V resistive circuit. The circuit current when the contacts are closed varies from 5A to 21A. The strength of a radial magnetic field for rotating break arcs changes. Arc duration is investigated. Then rotational frequency, arc length and Lorentz force when the periodic rotation of break arcs starts are analyzed to investigate the conditions required to rotate break arcs. The following results are obtained. The arc length L when the rotational motion of the break arc starts is almost constant at a constant magnetic flux density with an increase in circuit current. The arc length L decreases with an increase in the magnetic flux density of the radial magnetic field. The rotational motion of break arcs starts when the arc length L reaches a certain value determined by magnetic flux density. Rotational frequency and Lorentz force increase linearly with an increase in circuit current.

High Efficiency Radial Passive Magnetic Bearing

Passive magnetic bearing with Halbach array is presented in this paper. The array uses permanent magnets with radial and axial magnetization to augment the magnetic field on one side of the array and cancel it on the other side. The design of the bearing consists of ring-shaped magnets of 60x70 mm and 75x85 mm with different orientation of magnetization. The designed passive magnetic bearing has air gap of 2.5 mm, stiffness 129297 N/m and maximal value of load 200 N. The bearing ensures magnetic levitation and stabilization of rotor in a work point. The paper presents the design of the passive magnetic bearing as well as the experimental setup together with investigation results.

Realistic Subsurface Anomaly Discrimination Using Electromagnetic Induction and an SVM Classifier

The environmental research program of the United States military has set up blind tests for detection and discrimination of unexploded ordnance. One such test consists of measurements taken with the EM-63 sensor at Camp Sibert, AL. We review the performance on the test of a procedure that combines a field-potential (HAP) method to locate targets, the normalized surface magnetic source (NSMS) model to characterize them, and a support vector machine (SVM) to classify them. The HAP method infers location from the scattered magnetic field and its associated scalar potential, the latter reconstructed using equivalent sources. NSMS replaces the target with an enclosing spheroid of equivalent radial magnetization whose integral it uses as a discriminator. SVM generalizes from empirical evidence and can be adapted for multiclass discrimination using a voting system. Our method identifies all potentially dangerous targets correctly and has a false-alarm rate of about 5%.

A Comparative Study of Two Permanent Magnet Motors Structures with Interior and Exterior Rotor

Currently, the permanent magnet motors PMM represent an attractive solution in the electric traction field, thanks to their higher performances than other electric motors. In this context, this work represents an analytical study and validation by the finite element method of two configurations, the radial flux permanent magnet syn chronous motors with exterior rotor PMSMER and with interior rotor PMSMIR. This paper is divided into two sections: In the first section, we represent the analytical study based on electromagnetic law of the two structures PMSMER and PMSMIR. In the second section, we represent a comparative study of the two structure performances.

Prediction of Torque Pulsations in Brushless Permanent-Magnet Motors Using Improved Analytical Technique

Prediction of Torque Pulsations in Brushless Permanent-Magnet Motors Using Improved Analytical TechniqueTorque pulsations have prominent effects on the performance of brushless permanent- magnet (PM) machines. There are different sources of torque ripples in PM motors. These torque pulsations depend on the shape of the flux density distribution in the airgap region. For predicting the open-circuit airgap field distribution in brushless PM motors, a two dimensional (2-D) analytical method, in which the direction of magnetization, either radial or parallel and the effect of the stator slot-openings are taken into account, is used. The method uses an improved 2-D permeance model. In order to evaluate the accuracy of this method, a 2-D time-stepping FEM coupled with the two motion equations is used. A 3-phase, 36-slot, 4-pole, 5 HP, brushless PM motor is modeled by two methods. In this analysis both, the radial and parallel magnetization of the brushless motor are considered. The results obtained by the analytical method are compared with those obtained by FE analysis that shows the valuable accuracy of the analytical method for performance calculations in design and optimization processes.

Design and Control of Hybrid-type Three-pole Active Magnetic Bearings Using Redundant Coordinates

Recently, the design of active magnetic bearings (AMBs) for miniaturized industrial applications puts much emphasis on small size and low-power consumption as well as low-cost system production. In this paper, a novel hybrid type three-pole AMB system is proposed, which is divided into two bearing parts: a three-pole radial AMB and an axial permanent magnet bearing. The radial AMB consists of three active main poles with three coil windings, three sub-poles with radial permanent magnets, generating bias flux, and three Hall diodes, measuring the rotor position. The permanent magnet bearing is made of two facing axially polarized ring-type permanent magnets for passive stability in the axial and angular motion. Compared with the conventional four- or eight-pole AMB, the hybrid three-pole AMB system reduces the power consumption with fewer power amplifiers and is suitable for smaller-sized AMBs. The primary problem in modeling and control of the three-pole AMB in the conventional Cartesian coordinates is the strong coupling in magnetic flux generated by three main and sub-poles. Consequently, the system becomes strongly nonlinear with respect to control inputs as well as states. To resolve this difficulty in treating the strong nonlinearity in the conventional Cartesian coordinates, we introduce the redundant coordinates along with three-pole configuration for modeling and design of controller. Based on the redundant coordinates, three identical decoupled proportional—derivative controllers can be applied, which is very simple compared with previous nonlinear control algorithms developed for three-pole AMBs. Experiments are also carried out with a prototype AMB system to validate the proposed design and control concept based on the redundant coordinates.

The effect of magnetic configuration on ion acceleration from a compact helicon source with permanent magnets

Plasma production and emergent ion beam formation were examined in a compact helicon plasma source with different configurations of permanent magnets. Source modification employing a cylindrical ferrite assembly (CFA) with radial magnetization was found to produce high-density plasmas over a broad pressure range, but the ion beam was generated only at sub-millitorr pressures and provided that a pressure difference was set up between the discharge and the drift chambers. The modification employing the near field of a single annular ferrite (AF) was ineffective in both dense plasma and ion beam generation. The modification employing a combination of the AF with the CFA was found to be the most efficient for ion acceleration. It generated a fast ion beam with an energy of up to 200 eV in the sub-millitorr pressure range, and could produce the accelerated ions even in the millitorr range.

Force and Stiffness of Passive Magnetic Bearings Using Permanent Magnets. Part 2: Radial Magnetization

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper deals with the calculation of the force and the stiffness between two ring permanent magnets whose polarization is radial. Such a configuration corresponds to a passive magnetic bearing. The magnetic force exerted between ring permanent magnets is determined by using the Coulombian model. The expressions obtained are semianalytical and we show that it is not possible to find an exact analytical expression of the force between two ring permanent magnets. Then, thanks to these semianalytical calculations, the ring dimensions are optimized in order to have a great force or a great stiffness. Moreover, we show that the relative position of the rings for which the force is the strongest depends on the air gap dimension. This result is new because the curvature effect is taken into account in this paper. We can say that such semianalytical expressions are more precise than the numerical evaluation of the magnetic forces obtained with the finite-element method. Moreover, semianalytical expressions have a low computational cost whereas the finite-element method has a high one. Thereby, as shown in this paper, such calculations allow an easy optimization of quadripolar lenses or devices using permanent magnets. </para>

New analytical solution for the analysis and design of permanent magnet thrust bearings

On the basis of the current sheet model, a new analytical solution for permanent magnet (PM) bearings is developed. Compared with analytical methods based on the coupling energy model and the magnetic dipole model, the proposed one is more physically intuitive and convenient for engineering designers. According to the analytical model, the thrust characteristics of a novel PM thrust bearing is studied and verified by finite element analysis (FEA). In the proposed thrust bearing configuration, the rotor is composed of stacked PM rings with alternative axial magnetization directions, and the stator with alternative radial magnetization directions while copper rings are used to separate adjacent PM rings. A prototype PM thrust bearing with the proposed configuration is designed and fabricated. The performances of the PM thrust bearing are experimentally validated. It is shown that the calculation accuracy of the presented analytical solution is satisfying.

Magnetic Field Created by Tile Permanent Magnets

This paper presents an analytical calculation of the three components of the magnetic field created by tile permanent magnets whose magnetization is either radial or axial. The calculations are based on the Coulombian model of permanent magnets. The magnetic field is directly calculated, without the magnetic potential. Both axial and radial magnetization of the tiles are considered. The expressions obtained give the magnetic field in all the space. Such analytical expressions are very useful for the design and optimization of many industrial applications.

Characteristics of spatial magnetic torque of an intestine capsule micro robot with a variable diameter

A drive and control method is put forward for a variable diameter capsule micro robot to screw forward in intestine using magnetic coupling between an inner actuator inside the robot and the rotational magnetic field generated by a rotating outer actuator. The structures of the outer and inner actuators are magnet cylinders with multiple magnetic poles in tegular shape alternating with dissimilar radial magnetization. An universal mathematical model of magnetic torque at eccentric state is established based on the equivalent magnetic charge method, and the characteristics of magnetic torque with respect to structural parameters of actuators are theoretically studied. Experiments show that the driving method features advantages such as powerful magnetic torque, high safety, reliability, etc. The driving ability of the variable diameter capsule micro robot is greatly improved by its automatic radial clearance compensation. The magnetic drive system has a promising prospect of medical applications in intestine.

Analytical Solution of the Magnetic Field in Permanent-Magnet Motors Taking Into Account Slotting Effect: No-Load Vector Potential and Flux Density Calculation

We present a general computation taking into account the slotting effect on the no-load magnetic field distribution in multipole surface mounted permanent-magnet motors (SMPMM). A new analytical solution based on 2-D analysis in polar coordinates is developed. It includes both radial and parallel magnetization and the main originality is to consider the stator slotting. The saturation effect of the magnetic circuit is neglected. The 2-D analytical calculation of the no-load magnetic field with the slotting effect has been validated by a corresponding finite-element analysis (FEA). The analytical results are in very good agreement with those obtained by the FEA, considering both amplitude and waveform.

Characteristics of Magnetic Torque of a Capsule Micro Robot Applied in Intestine

A wireless drive and control method using rotational magnetic field on a capsule micro robot is proposed, and both outer and inner actuators are Nd-Fe-B magnet cylinders with multiple magnetic poles in tegular shape alternating with dissimilar radial magnetization, through magnetic coupling with rotational magnetic field generated by the rotating outer actuator, the capsule robot is rotated by an embedded inner actuator, and axial thrust is generated by fluid dynamic pressure distributing on outer surface of the robot with spiral blade, thus the screw motion of the micro robot in intestine is realized. Mathematical model on magnetic torque is established based on equivalent magnetic charge method, and the characteristics of magnetic torque with respect to structural parameters of actuators and swimming effect of the robot are studied theoretically and experimentally.

Torque in permanent magnet couplings: Comparison of uniform and radial magnetization

We present a three-dimensional study of the torque transmitted between tile permanent magnets uniformly magnetized. All this study is based on the Coulombian model. The torque is calculated semianalytically by considering all the surface densities that appear on the tiles. In addition, no simplifying assumptions are done in the expressions given in this paper. Consequently, the evaluation of the torque is very accurate and allows us to show the drawbacks of using tile permanent magnets uniformly magnetized instead of using tile permanent magnets radially magnetized. Such an approach is useful because it allows us to realize easily parametric studies.

Strong stray fields in magnets with a nonuniform distribution of the magnetization

Stray fields produced by magnets in the form of a cylinder in which the vector of magnetization at each point is directed along the cylinder radius have been calculated. It was assumed that this distribution of magnetization was achieved due to the presence of a radial crystalline texture and the related magnetic anisotropy with a large field of the uniaxial anisotropy HK. It has been shown that the greatest stray fields are reached on the surface of the magnet at points that are located near its axis, and the limiting value of the point field is equal to 4πMSln(a/r). It has been established that in magnets with a radial magnetization the region of localization of strong fields H > 4πMS substantially exceeds that characteristic of the systems of magnets with a uniform magnetization.

Non-uniform RKKY magnetism in thin wires

Analytical mean-field continual model of RKKY (Ruderman–Kittel–Kasuya–Yosida) magnetism in thin (nanosized) wires is considered. The spatial distribution of the magnetization is described by the nonlinear integral equation. Its solution delivers the radial magnetization distribution that occurs to be not only highly non-uniform but significantly non-monotone as well. The concrete form of the distribution depends on the wire radius, the interaction length, and concentrations of magnetic impurities and itinerant charge carriers. Results could be used for describing properties of nanosized systems based on the diluted magnetic semiconductors.

Optimal design of stator interior permanent magnet machine with minimized cogging torque for wind power application

This paper proposes a new approach to minimize the cogging torque of a stator interior permanent magnet (SIPM) machine. The optimization of stator slot gap and permanent magnet is carried out and the cogging torque ripple is analyzed by using finite element analysis. Experiments on a prototype machine verify the theoretical analysis. A comparison between the improved SIPM generator and a radial flux permanent magnet synchronous generator for a 3-MW wind turbine is carried out. It shows that the proposed SIPM generator has the advantages of higher power density and lower cost.

Effect of magnetization direction on irreversible magnet demagnetization in brushless dc motor

The magnetization direction of a permanent magnet is an important variable in the design process of a brushless dc motor. This paper describes the effect of the magnetization direction on the various characteristics. Especially, we concentrate on the irreversible demagnetization characteristic of a permanent magnet. Two kinds of magnetization direction (radial and parallel direction) and finite element method are used to analyze the effect. From the simulation and experimental results, we suggest that the radial magnetization direction has more advantage in terms of the irreversible magnet demagnetization.

An original analytical expression of the maximum magnet thickness in surface mounted permanent magnet motors

An exact two-dimensional (2-D) analytical model (AM) of slotless permanent magnet (PM) machines in polar coordinates is used to determine the analytical equations of the air-gap flux density at no-load operation. The authors show that, for a radial magnetization, there is an optimal magnet thickness which permits to maximize the no-load flux density. In order to use easily and directly this optimal value during the design of surface mounted PM motors (SMPMM), the authors propose an original analytical expression of this maximum magnet thickness that have been obtained by interpolation of the values given by several analytical computations. This interpolation function could be applied to SMPMM having a parallel or radial magnetization direction.