Permanent Magnet Rings Research Articles

Cylindrical linear pulse motor with interior permanent magnet mover

The advantages of the conventional cylindrical linear pulse motor (C-LPM), which has a ring permanent magnet between the A- and B-phase stators, are its simple magnet shape and small motor diameter; the disadvantages are the thrust imbalance resulting from the magnetic flux path of the outer poles being longer than that of the inner poles. This thrust imbalance decreases the pull-in thrust and increases the positioning error. In this paper, a new C-LPM with an interior permanent magnet mover which reduces this thrust imbalance is proposed. Steady and dynamic thrust are also examined and a magnetic equivalent circuit is discussed. It is shown that a C-LPM with an interior permanent magnet mover effectively improves the thrust imbalance and the dynamic thrust.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A 2-D treatment of the eddy currents induced by transversal oscillations of permanent magnet rings in conducting axisymmetric plates

It is shown that magnetic field and eddy current calculations in axisymmetric systems can still be performed two-dimensionally if the axial symmetry is disturbed by small displacements perpendicular to the symmetry axis of the magnetic field source. Such a situation occurs for instance when the rotor of a permanent magnetic bearing oscillates transversally to the rotation axis. By using appropriately adapted 2-D finite element programs the proposed method allows the computation of the eddy current losses in certain devices used for the damping of such oscillations. Numerical results are compared with experimental data. >

Stacked structures of passive magnetic bearings

The stiffness of magnetic bearings composed of only two permanent magnet rings is limited. To increase this stiffness, stacked structures are used. Conventional stacking is obtained by placement of the magnetizations in opposition. This article presents another type of stacking with rotating magnetization direction (RMD), which improves the stiffness by about a factor of 2 in comparison with the conventional stack.

Variable magnetic circuit torque sensor

This paper presents an original torque sensor structure using the properties of magnetic circuits, including permanent magnets. The torque is measured through the torsion of the transmitting shaft. The torsion is proportional to the torque. Considering two points of the shaft on the same line in absence of torque, the information is given by the twisting angle in the presence of a torque. A rotating magnetic circuit yields an angle representative signal. This circuit is deformed by the shaft torsion. The reluctance varies and so does the magnet operating point. The induction is measured in an airgap by a statoric galvanomagnetic device. The magnetic field source is an axial permanent magnet ring. Two iron-toothed rings, fixed to the driving and driven part of the shaft, respectively, and separated by an airgap make up the variable part of the magnetic circuit. The teeth get out of line whenever a torque is applied. The galvanomagnetic device measures an uniform induction and so delivers a modulation free signal, i.e., rotation independent. Because of the periodic toothed structure, the induction varies periodically with the twisting angle. The sense of the variation is the same over half a period or half a pitch. The variation form depends on the teeth design. Operating interval is to be chosen equal to or smaller than the half pitch.

Optimization studies on magnetic field geometry for planar magnetron sputtering targets

The present study deals with the design aspects of planar magnetron sputtering targets. A permanent ring magnet with modified pole piece geometry has been used for maximum ionization efficiency. The efficiency of electron containment on the target surface has been evaluated in terms of current at the electrically isolated substrates. The details of the relation between the magnetic field strength and field geometry on the ionization currents and operating pressure have been discussed. The best among the designs studied, when operated at a pressure of $8A—10^-^3$ Torr resulted in a deposition rate of about 2000 A/min at a current density of 4 mA/cm2. The substrate temperature rise was about 20°C under these conditions. The design details of the magnetrons, experimentation for evaluating the electron containment have been discussed in this article.

A new coincidence technique for vacuum ultraviolet photoelectron spectroscopy of neutral clusters in a molecular beam

The magnetic bottle photoelectron spectrometer principle has been employed for the study of neutral clusters in a seeded supersonic molecular beam. Mass selectivity is achieved by correlating each detached photoelectron to the cluster cation that is produced simultaneously. The necessary high detection probabilities for both particles, the photoelectron and the cluster ion, are achieved by time-of-flight spectrometers for both channels. The collection efficiency of the magnetic photoelectron spectrometer is increased to ≊80% of 4π by combining a permanent ring magnet, which produces an inhomogeneous field to parallelize the electron trajectories, with a 730-mm-long coil that guides the electrons by a weak, homogeneous field through the flight tube towards a scintillation detector. An advanced data acquisition electronics is described that is capable of recording and storing simultaneously photoelectron-photoion coincidence spectra of those neutral clusters that have sufficient intensity in the molecular beam.

4703276 Permanent magnet ring assembly for NMR imaging system and method for using such assembly

An NMR imaging system includes apparatus for producing a uniform magnetic field in a predetermined volume. Such apparatus includes a ring assembly having an axial extent L defined by a plurality of nonmagnetic rings, each having an axis and positioned side-by-side so that the axes of the rings are colinear and define the axis of the ring assembly. A plurality of discrete permanent magnet segments are angularly mounted within each ring for defining a central coaxial aperture. Each segment in a ring has a easy axis of magnetization whose orientation is functionally related to the angular position of the segment in the ring. Each segment has inner and outer edges that are nominally located at distances r 1 and r 2 , respectively, from the axis of the ring from which it is mounted. The inner free ends of the segments of all of the rings define a central aperture of length L within the ring assembly. Finally, an adjustment is provided for moving the segments in each ring such that the distance r 1 and r 2 of each segment are non-uniformly, but functionally related to the axial extent L of the assembly.

Characteristics of ring permanent magnet bearing

Permanent magnet bearings are useful for elements of super flywheels and super high vacuum pumps because of their simple construction and no losses. This paper describes a calculation method for forces between pairs of ring permanent magnets with small displacements from a center line of equilibrium. Test data on stiffness, thrust force and damping constant were used to verify the calculation. From this method, we developed a lower thrust force, or even repulsive type, permanent magnet bearing.

The Electron Beam Ion Source and Some Possibilities for Improvement

Considering basic properties of the EBIS, as vacuum requirements, ion yield, and emittance, it is pointed out, that the EBIS - as proposed by Donets - is restricted in priciple to a poor yield of highly charged ions, To overcome this, a concept for a dynamic is presented. This means, that the axial ion movement between first ionization and the extraction is delayed in order to give the necessary containment time at CW-operation. Realization seems to be possible by the partly permeable mirrors, produced by the axial alternating magnetic field of opposing permanent ring magnets, which also provide for electron focusing, considerable reduction of vacuum requirements, and saving of power consumption.