A New Interpretation of the Relationship Existing Between Demagnetizing Factor and Inductance

The paper discusses the methods by which knowing the size of the demagnetizing factor of a ferromagnetic core may assist in evaluating the inductance of an inductor assembled by winding a coil around the core. The particular method of evaluation developed in the present work is not conventional. The inductor coil and core assembly, whose inductance is sought, is regarded here as a pickup system located in a magnetic field generated by relatively far away sources. An approach similar to the one employed for obtaining the radiation impedance in antenna engineering (‘‘the induced emf metbod’‘) is then employed in order to evaluate the self inductance of the pickup system. The method is exemplified by employing the duality existing between a short electric dipole antenna and a cored loop (magnetic dipole) whose coil is wound around the central region of a straight ferromagnetic core. The results obtained by the present method are demonstrated to be identical to those obtained by the conventional method. Practical advantages of the present method are also discussed. The present method appears more general than the conventional method. It is not limited (like the conventional method) to special core geometries of long ellipsoids and long cylinders.