Mutual inductance between two coils
How strongly are these two coils coupled?
- M
- Mutual inductance, H
- k
- Coupling coefficient
- L1
- First inductance, H
- L2
- Second inductance, H
LaTeX
M = k \sqrt{L1 \cdot L2}Method
- Convert both inductances to henries.
- Take the geometric mean of the two — √(L₁ × L₂). This is the mutual inductance two perfectly coupled coils would have.
- Multiply by the coupling coefficient k to scale that ideal figure down to what these two coils, at this separation and alignment, actually achieve.
Assumptions
- k is supplied, not derived from geometry. Estimating it from coil spacing, core material and alignment is a separate, harder problem this calculation does not attempt — it takes k as a measured or assumed figure.
- k cannot exceed 1, which is the theoretical limit of perfect coupling; a value above that is not physically possible for two real coils and the result should not be trusted.
- Both coils are linear — neither core is near saturation, where its effective permeability, and so its inductance and coupling, would fall.