Magnetic field strength, in Gauss or Tesla, can be calculated at any distance from the end of a magnet. Results are for field strength on-axis, at a distance “Z” from a pole of the magnet.
These calculations are appropriate for “straight line” (referring to the Normal, B versus H hysteresis loop) magnetic materials such as sintered and bonded ferrite, fully dense neodymium-iron-boron and sintered samarium cobalt magnets.
Permeance Coefficients (Pc) are important in material selection to ensure optimal design. The Permeance Coefficient of a magnet is also referred to as the “operating slope”, load line or B/H of the magnet and often, but not always, refers to the magnet in open circuit condition. In open circuit, the Pc is calculated from the dimensions of the magnet and represents the Pc of the magnet in open circuit condition, that is, with no other permanent or soft magnetic material “nearby”.
Starting in the 1960’s and as a result of the development of ferrite magnets with a “square” intrinsic hysteresigraph curve (“straight” Normal curve), R.I. Joseph, E. Schlomann and others proposed calculations based on uniform magnetization throughout the magnet volume. More recently, additional calculations have been reported by Chen, Pardo, Sanchez, and others from the University of Madrid, Spain.
The Arnold web calculations are based upon these publications and approximations of the effective length of the material, Le, which is determined by material characteristics, and generally conforms to values returned from calculations within commercially available FEA software.
Please select which Permeance Coefficient calculation best suits your application by referring to the diagrams.