This is an popular coil geometri used in todays wireless charger circuits. The formula used in this calculation is based on the Harold A. Wheeler approximations for air core flat spiral coil inductor. …where: 1 inch = 0,0254m=2,54cm = 25,4mm. This formula applies at ‘low’ frequencies (<30MHz) using enameled copper wire. Some people call it “magnet wire”. Click on image …

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## Planar spiral coil inductor design

The first approximation is based on a modification of an expression developed by Wheeler; the second is derived from electromagnetic principles by approximating the sides of the spirals as current-sheets; and the third is a monomial expression derived from fitting to a large database of inductors (and the exact inductance values). All three expressions are accurate, with typical errors of …

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