Permeance

Permeance, in general, is the degree to which a material admits a flow of matter or energy. Permeance is usually represented by a curly capital P: ${\mathcal {P}}$.

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 ${\mathcal {P}}$ is defined as the reciprocal of magnetic reluctance ${\mathcal {R}}$ (in analogy with the reciprocity between electric conductance and resistance):

${\mathcal {P}}={\frac {1}{\mathcal {R}}}$

which can also be re-written:

${\mathcal {P}}={\frac {\Phi _{B}}{NI}}$

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):

${\mathcal {F}}=\Phi _{B}{\mathcal {R}}=NI$

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 conductivity):

${\mathcal {P}}={\frac {\mu A}{\ell }}$

Where:

μ = Permeability of material

A = Cross-sectional area

$\ell$ = 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.

See also

• Dielectric complex reluctance
• Reluctance

External articles and references

Electromagnetism

• Properties of Magnetic Materials (units of magnetic permeance)

Material science

• Bombaru, D., Jutras, R., and Patenaude, A., "Air Permeance of Building Materials". Summary report prepared by, AIR-INS Inc. for Canada Mortgage and Housing Corporation, Ottawa, 1988.