MODERN PERMANENT-MAGNETS FOR APPLICATIONS IN ELECTROTECHNOLOGY

Permanent magnets (PMs) are vital components of many electromechanical machines and electronic devices, but they are usually hidden in subassemblies. System designers and end users often give no thought to how choice and use of the PM material affect performance, size, and cost of the product. This paper describes the range of materials and properties now at the disposal of design engineers and the place of different magnets in electro-technology, with attention to engineering and economic aspects. Revolutionary developments have recently occurred in the old field of permanent magnetism. Hard ferrites became an abundant inexpensive magnet material while the rare-earth magnets raised the highest available energy products 4 to 5-fold and coercivity by an order of magnitude. As a consequence, a rapid broadening of magnet uses is now occurring; traditional devices are miniaturized, new applications and design concepts are evolving. Trends and examples are discussed in this paper. A confluence of recent developments in magnets, power semiconductors and microprocessors is particularly fruitful in the area of drives and motion control. We also assess currently evolving PM materials, production processes, prospects for new, still “better” magnets, as well as ultimate upper limits for permanent magnet properties. © 1990 IEEE