At COMPEL 2013, we presented an alternative self-resonant structure that can overcome various challenges associated with litz wire coils in the MHz frequency range. Link to full paper

The self-resonant structure is made of many layers of C-shaped thin foil conductors (much thinner than a skin depth) stacked in alternating orientation. A ballast capacitance is introduced by placing thin dielectric layers between adjacent conductor layers to force equal current sharing among the thin conductor layers.

This self-resonant structure has several advantages over conventional solid or litz wire coils connected to an ad

1. Lower proximity effect extending into the MHz frequency range because of capacitive ballasting and because foil conductors are available in much smaller thickness than the skin depth
2. Elimination of high resonating-current termination between inductor and capacitor in conventional resonator
3. Elimination of electrode plate loss associated with external capacitor; the capacitance is integrated into the structure.

These advantages result in a calculated Q value of 1368 at 160 kHz for a structure with an 18 cm diameter.