Abstract: An apparatus (10) for altering the magnetic state of a permanent magnet comprises a coil inductor (26) for generating and applying an induced magnetic field to the permanent magnet. The coil inductor (26) is provided in circuit between two charge storage elements (20, 24). The apparatus also comprises a discharge control circuit (28) for transferring charge alternately in opposed directions between the storage elements (20, 24) though the coil inductor (26) to generate a series of alternating polarity magnetic field pulses (167, 191) of decreasing magnitude in the coil inductor (26) or to generate a single magnetic pulse of relatively high strength. The apparatus (10) can be operated as either a magnetising or demagnetising device and is capable of demagnetising a column of 200 or more magnets.

Abstract: A method and apparatus for determining remanence and coercivity of high strength rare earth magnets, without full determination of their hysteresis characteristics and subsequent computation, enables high speed, high throughput testing of such magnets in a production facility. The magnets are first fully magnetized by capacitor discharge through a pulsing magnetizing coil, if not already fully magnetized, and their remanence can be noted at zero applied field. Then the magnets are progressively demagnetized, again by capacitor discharge through a pulsing coil, and, with the state of magnetization of the magnets and the strength of demagnetizing field continuously monitored, note is taken of the strength of the demagnetizing field when the magnetization of the magnet is reduced to zero. Based on this sole measurement, the coercivity of the magnet is derived.