Permanent magnet applications

The main uses of permanent magnets are covered either by the range of cast and magnetically treated alnico alloys or by the several grades of sintered barium/strontium hexaferrite, but minority materials have their special applications and continue to develop. Three different technical classes of permanent magnet applications can be distinguished. Firstly, magnets working in a magnetic circuit of static reluctance, e.g., speakers, moving-coil measuring instruments, microwave devices, separators, etc. Secondly, those working in a varying self-demagnetizing field due to change of circuit reluctance, such as clamping and holding magnets which range from planning-board indicators to large chucks for machine-tools. Thirdly, magnets which work in both a self-demagnetizing field and a varying externally produced field, as in motors, generators, the several types of magnetic couplings, and magnetic suspensions. For each of these three classes the basic design principles are indicated and typical applications are described. Additionally, there are uses for high-hysteresis permanent magnet materials without premagnetization, as in hysteresis motors.