A composite magnetic core formed of a high permeability material and a lower permeability, high saturation flux density material prevents core saturation without an air gap and reduces eddy current losses and loss of inductance. The composite core is configured such that the low permeability, high saturation...http://www.google.com/patents/US6980077?utm_source=gb-gplus-sharePatent US6980077 - Composite magnetic core for switch-mode power converters
