permeance [′pər·mē·əns]
Permeance
(electromagnetism)
A characteristic of a portion of a magnetic circuit, equal to magnetic flux divided by magnetomotive force; the reciprocal of reluctance. SymbolizedP.
Permeance
The reciprocal of reluctance in a magnetic circuit. It is the analog of conductance (the reciprocal of resistance) in an electric circuit, and is given by
(1) 
Eq. (1), where B is the magnetic flux density, H is the magnetic field strength, and the integrals are respectively over a cross section of the circuit and around a path within it. From Eq. (1), it can be shown that Eq. (2) is valid, where A
(2) 
is the cross-sectional area of the magnetic circuit, l its length, and μ the permeability. If the material is ferromagnetic, as is often the case, then μ is not constant but varies with the flux density and the complete magnetization curve of B against H may have to be used to determine the permeance. See Reluctancepermeance
A measure of a material’s resistance to water-vapor transmission, expressed in perms. Equal to the ratio of (a) the rate of water vapor transmission through a material or assembly between its two parallel surfaces to (b) the vapor pressure differential between the surfaces.
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