Gap design for nonlinear ferrite cores to maximize inductance

Conventional design of ferrite-cored inductor employs air gaps to store magnetic energy. In this work, the gap length is allowed to be smaller than the conventional value so that the nonlinear ferrite material is biased in the region with low permeability and, hence, significant energy density. A peak in the inductance-gap relationship has thus been uncovered where the total energy stored in the gaps and the core is maximized. A reluctance model is formulated to explain the peaking behavior, and is verified experimentally. Curves of inductance versus gap length are generated to aid the design of swinging inductance and reduce the core size.