Permanent magnet devices

The largest single application of anisotropic hexaferrites is in loudspeakers, Fig. 5.1. The ferrite is an anisotropic ring, axially magnetised. The signal to be transformed to sound, typically from an amplifier, flows through the coil fixed to the end of the speaker cone the interaction 

Rolling technology to produce radially magnetised rotors for stepping motors (Torii, Kobayashi Okuda, 1982), 

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Magnetic yokes in permanent magnet devices, such as lifting and holding magnets, loudspeakers... 

The principle upon which permanent-magnet devices operate is to establish the magnetic lines of force or flux from the permanent magnets through the workpiece when switched on, and... 

Plate Magnets. Plate magnets (Fig. 6a) are simple devices usually mounted in the bottom of a chute or duct. These magnetized plates are manufactured in various models and are normally of the permanent magnet type. The largest units provide protection to about 115 mm of material depth, at chute angles of up to 45° from the horizontal. 

Drum and Pulley Magnets Since Thomas Edison invented and developed the magnetic pulley for the concentration of nickel ore, drums and pulleys have become the most common types of magnetic separators. These devices can be built with either a permanent magnet or an electromagnet, and the drum separator can operate with... 

In 1821 Michael Faraday sent Ampere details of his memoir on rotary effects, provoking Ampere to consider why linear conductors tended to follow circular paths. Ampere built a device where a conductor rotated around a permanent magnet, and in 1822 used electric currents to make a bar magnet spin. Ampere spent the years from 1821 to 1825 investigating the relationship between the phenomena and devising a mathematical model, publishing his results in 1827. Ampere described the laws of action of electric currents and presented a mathematical formula for the force between two currents. However, not everyone accepted the electrodynamic molecule theory for the electrodynamic molecule. Faraday felt there was no evidence for Ampere s assumptions and even in France the electrodynamic molecule was viewed with skepticism. It was accepted, however, by Wilhelm Weber and became the basis of his theory of electromagnetism. 

The direction of rotation depends on the direction of the current in the coil, and thus the instrument is only suitable for D.C. It is, however, possible to incorporate a full-wave rectifier arranged as shown in Figure 17.11 in order to allow the instrument to measure A.C. quantities. The quantity measured is the RMS value only if the waveform of the current is truly sinusoidal. In other cases, a considerable error may result. In principle, the scale is linear but, if required, it can be made non-linear by suitably shaping the poles of the permanent magnet. The instrument reading is affected by the performance of the rectifier, which is a non-linear device, and this results in the scale also being non-linear. The error when measuring D.C. quantities can be as low as 0.1 per cent of full-scale deflection and instruments are available for currents between microamperes and up to 600 A. 

Cathodic protection apparatuses are well proven, widely used devices and are not to be confused with magnetic devices gadgets ) or other similar but generally less than satisfactory items of capital equipment. Cathodic protection devices reverse the tendency of a metal to go into solution at the anode (corrosion) by the application of a counter-potential. This counter-potential or electromotive force (EMF) is provided either from a permanent external source such as a battery or rectifier or from the installation of a sacrificial anode. 

Superior water conditioners. These are tubular-shaped devices that employ permanent magnets (no electrical connection). The devices are designed with a cobalt-content alloy core, arranged so that water flows around the magnetic core and perpendicular to the magnetic fields. 

The LKC eliminates many problems that are presented by the utilization of permanent magnetic or electrostatic water treatment devices of which you may have heard. ... 

T. Miyamoto, H. Sakurai, H. Takabaya-shi, M. Aoki 1989, (A development of a permanent magnet assembly for MRI devices using Nd-Fe-B material), IEEE Trans. Magn. 25, 3907-3909. 

Samarium salts are used in optical glass, capacitors, thermoionic generating devices, and in sensitizers of phosphors. The metal is doped with calcium fluoride crystals for use in lasers. It also is used along with other rare earths for carbon-arc lighting. Its alloys are used in permanent magnets. 

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