Most SMPS use coupled magnetics of various kinds. While designing buck/boost and their isolated versions, construction of the coupled magnetic element is straight forward. In many of these converters the issue of discontinuous current (both on the input and output exist) . I came across literature which claim zero ripple using coupled inductors. The results are fascinating to say the least
However it requires the need of coupled inductors with coupling factors <1. Designs specifically mention critical values to be around 0.6. I don't seem to find any links for construction of such inductors.
How are such coupled inductors constructed? (what type of cores, winding detail etc.,)