As the current density is assumed constant along the length of each filament, the partial mutual inductance between two filaments of the two parallelograms is given by Neumann's formula
The partial mutual inductance between two parallelograms can then be calculated as the partial mutual inductance between two filaments, which is given by the Neumann's formula (3).
pf] between any two parallel filaments AB, ab in any relative position in space can be found from Neumann's formula (3), where [r.
According to Neumann's formula (4), the coupling coefficient can be controlled by the distance between two coils, the number of turns, and the radius of the coils.
Equation (4) is an approximated Neumann's formula for long distances of r [much less than] [d.