Magnetic properties of compressed powdered iron

This paper describes a new magnetic material which is peculiarly suited to the construction of cores in small inductance coils and transformers such as are used in a telephone plant. The requirements which were to be met involved a core material which should have a constant permeability, a small hysteresis loss, and a small eddy current loss within the range of magnetizing forces and frequencies which are met in telephonic operation. The material which was developed to meet these requirements is formed by fine grains of powdered iron, insulated and compressed. There are described the circumstances and experiments which led to this development and also the method of commercial production. Tables and curves are given showing the magnetic, electrical, and mechanical properties of the material.