Miniature ferrite cores

Abstract

Several performance advantages can be realized in ferrite memory cores by reducing the aperture size and the diameter ratio. Advantages which can be obtained are: lower drive currents, wider operating margins, lower back voltage, and greater packing density. The smallest cores produced by conventional core pressing technology have apertures of 180 μ and diameter ratios of 1.6. A new forming method has been developed for producing, in quantity, cores having apertures of 110 μ and diameter ratios of 1.36. Excess fragility is avoided by building the cores with two materials in concetric relationship. Both the inner magnetic layer and the outer nonmagnetic layer have thicknesses of 20 μ, leading to a physical diameter ratio of 1.7. In the process, a cylindrical monofilament is coated with successive layers of varnishes loaded with ferrite powders. Curing and cutting short lengths of this formed tubing produce green cores which are then fired to high temperature. The materials are chosen for compatibility of firing shrinkage, low interlayer reactivity, and zero magnetostriction. The inner magnetic layer has zero magnetostriction with the composition Fe1.62Mn0.80Cu0.45Zn 0.10Bi0.02La0.01O4. The nonmagnetic layer is Fe1.20Mn0.78Cu0.30Zn 0.70Bi0.02O4. © 1967 The American Institute of Physics.