Results can be output in various forms, including plots of vector magnetic potentials, flux density maps, and flux path plots. The basis of magnet design is the B-H curve, or hysteresis loop, which characterizes each magnet material. This curve describes the cycling of a magnet in a closed circuit as it is brought to saturation, demagnetized, saturated in the opposite direction, and then demagnetized again under the influence of an external magnetic field. A permanent magnet will have a unique, static operating point if air-gap dimensions are fixed and if any adjacent fields are held constant. Otherwise, the operating point will move about the demagnetization curve, the manner of which must be accounted for in the design of the device.
B r represents the maximum flux the magnet is able to produce under closed circuit conditions.
In actual useful operation permanent magnets can only approach this point. H c represents the point at which the magnet becomes demagnetized under the influence of an externally applied magnetic field. BH max represents the point at which the product of B and H, and the energy density of the magnetic field into the air gap surrounding the magnet, is at a maximum. The higher this product, the smaller need be the volume of the magnet. Designs should also account for the variation of the B-H curve with temperature.