Permeance

 ( Electric And Magnetic Fields In Matter ) 

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: .

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Electromagnetism In electromagnetism, permeance is the inverse of reluctance. In a magnetic circuit, permeance is a measure of the quantity of magnetic flux for a number of current-turns. 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 smaller cross section lengths. This concept is analogous to electrical conductance in the electric circuit.

Magnetic permeance is defined as the reciprocal of magnetic reluctance (in analogy with the reciprocity between electric conductance and resistance): $$\backslash mathcal\{P\}\; =\; \backslash frac\{1\}\{\backslash mathcal\{R\}\}$$

which can also be re-written: $$\backslash mathcal\{P\}\; =\; \backslash frac\{\backslash Phi\_\backslash mathrm\{B\}\}\{NI\}$$

using (magnetic circuit analogue of Ohm's law for electric circuits) and the definition of magnetomotive force (magnetic analogue of electromotive force): $$\backslash mathcal\{F\}\; =\; \backslash Phi\_\backslash mathrm\{B\}\; \backslash mathcal\{R\}\; =\; NI$$

where:

• , magnetic flux,
• , current, in amperes,
• , winding number of, or count of turns in the electric coil.

Alternatively in terms of magnetic permeability (analogous to electric conductivity): $$\backslash mathcal\{P\}\; =\; \backslash frac\{\backslash mu\; A\}\{\backslash ell\}$$

where:

• , permeability of material,
• , cross-sectional area,
• ℓ, magnetic path length.

The SI unit of magnetic permeance is the henry (H), equivalently, webers per ampere.

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

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See also

• Dielectric complex reluctance
• Reluctance

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Notes

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Electromagnetism

• Properties of Magnetic Materials (units of magnetic permeance)

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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.

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