In this paper, we present a modified self-resonant structure in which the layered conductors are made from standard PCB substrates with no vias. In order to reduce winding loss, these structures are made with foil layers much thinner than a skin depth, which makes the layers of the structure extremely difficult to handle. In these structures thin foil layers are separated by a dielectric material in order to form a capacitance that resonates with the inductance of the structure, while also forcing equal current sharing between conductors. Multi-layer self-resonant structures have been proposed as a low-cost method for creating high-Q coils for highfrequency wireless power transfer. The range and efficiency of wireless power transfer systems are limited by the quality factor of the transmit and receive coils used. Keep in mind the having an exact match to a published mi Value is unlikely due to material variation and measurement equipment differences. The resulting permeability number can then be matched up to a ferrite material by comparing the mi value published. This tool will calculate the permeability of a toroidal type core when the following values are entered by the user: three critical mechanical dimensions (outer diameter, inner diameter, part height), the number of passes through the aperture of the core, and the measured series inductance of the wound core. To evaluate the permeability, you will need insulated wire and some way to measure inductance with a 10kHz sinusoidal signal (in a pinch 1kHz-100kHz will yield a similar number for most materials). Calculating the initial permeability on the sample in question is the most reliable way to get an approximation of its material grade. This is the inductive portion of the complex permeability of a material measured specifically at 10kHz with a flux density of less than 10 gauss (sinusoidal excitation). The main characteristic differentiating Fair-Rite’s material grades is initial permeability.

Ferrite inductance calculator