Results 1 - 10 of 5223
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[en] Various permanent magnet arrangements to produce a uniform field for NMR tomography are discussed. Standard requirement is a full-body magnet with access diameter of at least 1 m and a non-uniformity of at most 100 ppm within a sphere of 0.5 m diameter. Magnet weight, material price and ease of construction are considered. The conclusion is that permanent magnet systems of reasonable weight and price produce a field of no more than about 0.2 T. A prismatic ferrite magnet design is proposed as the most feasible one. It generates a field of 0.15 T in a 1 m air gap, weighs 21 tonnes and requires about 800 thousand dollars worth of ferrite. (author). 1 ref.; 17 figs.; 2 tabs
[en] A compact Permanent Magnet Symmetric (PMS) lens which produces the axial magnetic field is studied. The proposed lens has no iron pole piece except for the return poles on both ends. It can produce the magnetic field on the axis more than the remanent field of the magnet material by the perpendicular field superimposition
[en] In this paper we investigate the torque performances of three prototypes of a magnetorheological clutch, whose operation is based on the relative movement of a permanent magnet with respect to a gap filled with magnetorheological fluid, are discussed. The clutch was already been presented by the authors in other papers. The analysed prototypes are based on the same layout and have different sizes (i.e. outer diameter and overall length). Two new performance indices are introduced to evaluate the clutch design, and are proposed as an alternative to the usually employed turn-up ratio for evaluating MR clutches and brakes. Measurements of the transmitted torque in different operating conditions were carried out on a purpose-built test bench. A brushless motor drove the primary shaft of the clutch, while the transmitted torque was measured by a torque-meters up to 1500 rpm. The experimental results are discussed and compared to those expected on the basis of simulations, showing a fairly good agreement. Some geometric parameters were found to have a great influence on the magnet shielding in the disengaged configuration. (paper)
[en] Response is given to various questions on alignment tolerances for the permanent magnet sextupoles (PMS's) in the damping rings. Consideration is given to rotational errors, strength/longitudinal placement errors, transverse placement errors, pitch/yaw or tilt errors, and harmonic field errors. Resulting error limits can be specified in terms of the maximum errors allowed in the distribution
[en] Helicon discharges are known for their ability to produce high densities of partially ionized plasma, their efficiency arising from an unusual mechanism of rf coupling. However, the requirement of a dc magnetic field has prevented their wide acceptance in industry. The use of permanent magnets greatly simplifies helicon sources, and arrays of small sources extend the use of helicons to the processing of large substrates. An eight-tube array was designed and constructed, and its density uniformity measured in a 53x165 cm2 chamber. Three innovations involved (a) the remote field of ring magnets, (b) a low-field density peak, and (c) rf power distribution. High-density plasmas uniform over large areas requires compatibility in all three areas.
[en] Highlights: • Impact on wind turbines due to fifth harmonic and sag content. • Converter topologies considered are two-level and three-level ones. • Controllers are based on PI and fractional-order methods. • New control strategy for the selection of output voltage vectors. • Balancing voltages in the DC-link capacitors. - Abstract: This paper deals with the computing simulation of the impact on permanent magnet synchronous generator wind turbines due to fifth harmonic content and grid voltage decrease. Power converter topologies considered in the simulations are the two-level and the three-level ones. The three-level converters are limited by unbalance voltages in the DC-link capacitors. In order to lessen this limitation, a new control strategy for the selection of the output voltage vectors is proposed. Controller strategies considered in the simulation are respectively based on proportional integral and fractional-order controllers. Finally, a comparison between the results of the simulations with the two controller strategies is presented in order to show the main advantage of the proposed strategy
[en] To increase the displacement stiffness and decrease power loss of double gimbals magnetically suspended control momentum gyro (DGMSCMG), this paper researches a new structure of axial passive magnetic bearing (APMB). Different from the existing APMB, the proposed APMB is composed of segmented permanent magnets and magnetic rings. The displacement stiffness and angular stiffness expressions are derived by equivalent magnetic circuit method and infinitesimal method based on the end magnetic flux. The relationships are analyzed between stiffness and structure parameters such as length of air gap, length of permanent magnet, height of permanent magnet and end length of magnetic ring. Besides, the axial displacement stiffness measurement method of the APMB is proposed, and it verified the correctness of proposed theoretical method. The DGMSCMG prototype is manufactured and the slow-down characteristic experiment is carried out, and the experimental result reflects the low power loss feature of the APMB. - Highlights: • A novel high stiffness axial passive magnetic bearing for DGMSCMG. • The proposed APMB is composed of segmented permanent magnets and magnetic rings. • The APMB is analyzed by EMCM and infinitesimal method based on the end magnetic flux. • The axial displacement stiffness measurement method of the APMB is proposed. • The DGMSCMG is manufactured and proved the correctness of theoretical analysis.
[en] This paper presents the effects of skewing the rotor teeth on the performance of an 8/6 doubly salient permanent magnet motor using a simple method, which utilizes the results obtained from the 2-D FE analysis. The optimum skewing angle is obtained as 12-15o for the least ripple torque without much reduction in the back-emf
[en] A Faraday isolator with a single magneto-optical element is constructed and experimentally tested. It provides the isolation ratio of 30 dB at an average laser radiation power of 650 W. These parameters are obtained by increasing the field intensity in the magnetic system of the isolator and employing a low-absorption magneto-optical element. (elements of laser devices)