Abstract :
The theoretical investigation of an earlier paper has been extended by a study of the effect of the shape of the demagnetization curve of a permanent magnet on its performance. This has been carried out in terms of the reduced co-ordinates, i.e. the ratio of B and H to their values at the remanence and coercive points respectively. It is shown that the performance can then be determined entirely by the curve factor and the magnet´s dimensions. In particular, all magnets of the same curve factor will give the same output in a given construction, providing that the quantities ABr and LHc are maintained constant. There are only three different curve factors to cover all the alloys which are commercially available. The smallest of these (0.42) applies to all the isotropic materials. Curve factors must lie between the values of 0.25 and 1.0, but the extreme values can only be reached when the ratio of coercive force to remanence is infinity or zero. The maximum curve factor obtainable when this ratio is known has been calculated. The use of remanence factor is preferable to curve factor in computation; so the four cases of magnet utilization have been evaluated in terms of the former, and the leakage coefficient. Curves have been plotted to illustrate these relationships. Apart from the case of static flux with full recoil, increases of remanence factor (or curve factor) produce increased useful energy when measured in terms of the product of remanence and coercive force. The exception gives a minimum for a remanence factor of 0.7, the value corresponding to the isotropic alloys. On the other hand, the utilization factor (useful energy in terms of BHmax) always decreases steadily for increases in remanence factor. Families of curves have been plotted for all four cases of magnet utilization and for each practical alloy. An example is given of the uses of these curves in a design problem.
