The windings of a fractal transformer follow a fractal patter, in this case the Koch curve. Primary winding is on one layer, secondary on another layer. See also: q-factor_and_l_for_koch_planar_transformer_-_stojanovic_et_al.png
The drawing was copied from: Goran Stojanović, Milan Radovanović, Vasa Radonić, A New Fractal-Based Design of Stacked Integrated Transformers, Active and Passive Electronic Components, Vol. 2008, 2008, Article ID 134805
koch_planar_transformer_-_stojanowic_et_al.png
You can use this image freely (there is no need to ask for explicit permission), but you must give the following credits:
Goran Stojanović, Milan Radovanović, Vasa Radonić, CC-BY-3.0.