# Mutual Inductance Between Two Same Axial Inductors

I was searching for few hours on this topic but I was unable to find any formula/research so I'm asking here. Please if this question is a duplicate let me know.

Right now I do not have the equipment to prove or deny the following formula I came up with.

I have two (same) tht axial inductors. Those in a 1/4w resistor-like shape (with PVC coating). I do not know the core material or the number of windings. But I'm trying to estimate the Mutual inductance M.

Knowing that inductance L of each inductor is given by:

L = u0 * ur * N^2 * A / l


And having the M impedance formula (found here: http://www.electronics-tutorials.ws/inductor/mutual-inductance.html)

M = u0 * ur * N1 * N2 * A / d


(Distance referred as 'l' in the article replaced with 'd' for clearance)

Assuming the following:

ur - all cores are of same material
N1 = N2
A - all cores areas are same


I came up that M of two same axial inductors with inductance L, length 'l' at distance 'd' is:

M = L * l / d


...sounds too simple, to be real... But is this correct? It mean that my 47uH inductors with l=2.9mm at a distance d=6mm has a mutual inductance M=22uH sounds huge?

• Flux must be shared and thus coaxial wound on the same core – Tony Stewart Sunnyskyguy EE75 Oct 19 '16 at 23:39