Permeance

Electromagnetism

In electromagnetism, permeance is the inverse of reluctance. Permeance is a measure of the quantity of flux for a number of current-turns in magnetic circuit. A magnetic circuit almost acts as though the flux is 'conducted', therefore permeance is larger for large cross sections of a material and smaller for longer lengths. This concept is analogous to electrical conductance in the electric circuit.

Magnetic permeance P is defined as the reciprocal of magnetic reluctance R (in analogy with the reciprocity between electric conductance and resistance):

P = 1 R

which can also be re-written:

P = Φ B N I

using Hopkinson's law (magnetic circuit analogue of Ohm's law for electric circuits) and the definition of magnetomotive force (magnetic analogue of electromotive force):

F = Φ B R = N I

Where:
Φ_B = Magnetic flux
NI = Current-turns, (current) × (number of turns of conductor to make a coil).

Alternatively in terms of magnetic permeability (analogous to electric conductance):

P = μ A ℓ

Where:
μ = Permeability of material
A = Cross-sectional area
ℓ = magnetic path length

The SI unit of magnetic permeance is "webers per ampere-turn", that is H (henry).

Materials science

In Materials science, permeance is the degree to which a material transmits another substance.