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Encyclopedia > Permeability (electromagnetism)

In electromagnetism, permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. Magnetic permeability is represented by the Greek letter μ. This term was coined in September, 1885 by Oliver Heaviside. Electromagnetism is the physics of the electromagnetic field; a field encompassing all of space which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles. ... Magnetization is a property of some materials (e. ... Current (I) flowing through a wire produces a magnetic field () around the wire. ... For other uses, see Mu. ... 1885 (MDCCCLXXXV) is a common year starting on Thursday of the Gregorian calendar (or a common year starting on Saturday of the 12-day slower Julian calendar). ... Oliver Heaviside (May 18, 1850 – February 3, 1925) was a self-taught English engineer, mathematician and physicist who adapted complex numbers to the study of electrical circuits, developed techniques for applying Laplace transforms to the solution of differential equations, reformulated Maxwells field equations in terms of electric and magnetic...


In SI units, permeability is measured in henries per metre, or newtons per ampere squared. The constant value μ0 is known as the magnetic constant or the permeability of vacuum, and has the exact value 4π×10−7 N·A−2. Cover of brochure The International System of Units. ... An inductor. ... The metre, or meter (U.S.), is a measure of length. ... The newton (symbol: N) is the SI unit of force. ... Current can be measured by a galvanometer, via the deflection of a magnetic needle in the magnetic field created by the current. ... The magnetic constant () is the permeability of vacuum. ...


Some materials, called ferromagnetic or ferromagnets, are highly magnetic by nature, relative to most materials. They are composed of a large number of very small magnetic units working together called domains. Domains are not always aligned, and they often act against each other to reduce the strength of the net magnetic field. Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ... A ferromagnet is a piece of ferromagnetic material, in which the microscopic magnetized regions, called domains, have been aligned by an external magnetic field (e. ... In physics, magnetism is a phenomenon by which materials exert an attractive or repulsive force on other materials. ...


If one puts the ferromagnetic material into an externally applied magnetic field, the domains tend to line up, so that the sum of the fields from the ferromagnet and the resulting magnetic field is higher in magnitude than the applied magnetic field alone.


Permeability in linear materials owes its existence to the approximation:

mathbf{M}=chi_mmathbf{H}

where chi_m , is a dimensionless scalar called the magnetic susceptibility. In physics and electrical engineering, the magnetic susceptibility is the degree of magnetization of a material in response to an applied magnetic field. ...


According to the definition of the auxiliary field, H

mathbf{B}=mu_0 (mathbf{H}+mathbf{M})=mu_0 (1 + chi_m)mathbf{H} = mu mathbf{H}

where

μ is the material's permeability, measured in henries per metre
B is the magnetic flux density (also called the magnetic induction) in the material, measured in teslas
H is the magnetic field intensity, measured in amperes per metre
M is the material's magnetization, measured in amperes per metre

The permittivity of free space (the electric constant) and the magnetic constant are related to the speed of light (c) by the formula: varepsilon_0mu_0 = frac{1}{c^2} An inductor. ... The metre, or meter (U.S.), is a measure of length. ... Current flowing through a wire produces a magnetic field (B, labeled M here) around the wire. ... Electromagnetic induction is the production of an electrical potential difference (or voltage) across a conductor situated in a changing magnetic field. ... SI unit. ... Current can be measured by a galvanometer, via the deflection of a magnetic needle in the magnetic field created by the current. ... The metre, or meter (U.S.), is a measure of length. ... Current can be measured by a galvanometer, via the deflection of a magnetic needle in the magnetic field created by the current. ... The metre, or meter (U.S.), is a measure of length. ... Permittivity is a physical quantity that describes how an electric field affects and is affected by a dielectric medium and is determined by the ability of a material to polarize in response to an applied electric field, and thereby to cancel, partially, the field inside the material. ... A line showing the speed of light on a scale model of Earth and the Moon The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness. It is the speed of all electromagnetic radiation...


Relative permeability, sometimes denoted by the symbol μr, is the ratio of the permeability of a specific medium to the permeability of free space μ0:

mu_{r} = frac{mu}{mu_{0}}

In terms of relative permeability, the magnetic susceptibility is:

chi_m = mu_r - 1 ,

χm, a dimensionless quantity, is sometimes called volumetric or bulk susceptibility, to distinguish it from χp (magnetic mass or specific susceptibility) and χM (molar or molar mass susceptibility).

Magnetic permeability & susceptibility for selected materials
Medium Susceptibility Permeability
Mu-metal 20,000 [1] 25,000 µN/A2 at 0.002 T
Permalloy 8000 [1] 10,000 µN/A2 at 0.002 T
Transformer iron with ρ=0.01 µΩ·m 4000 [1] 5000 µN/A2 at 0.002 T
Steel 700 [1] 875 µN/A2 at 0.002 T
Nickel 100 [1] 125 µN/A2 at 0.002 T
soft ferrite with ρ=0.1 Ωm source, ferroxcube 5000 µN/A2 < 0.1 mT
soft ferrite with ρ=10 Ωm source, ferroxcube 2500 µN/A2 < 0.1 mT
Platinum 2.65 × 10−4 1.2569701 µN/A2
Aluminum 2.22 × 10−5 [2] 1.2566650 µN/A2
Hydrogen 8 × 10−9
or 2.2 × 10−9 [2]		 1.2566371 µN/A2
Vacuum 0 1.2566371 µN/A2
Sapphire −2.1 × 10−7 1.2566368 µN/A2
Copper −6.4 × 10−6
or −9.2 × 10−6 [2]		 1.2566290 µN/A2
Water −8.0 × 10−6 1.2566270 µN/A2

Permeability varies with flux density. Values shown are approximate and valid only at the flux densities shown. Moreover, they are given for a zero frequency; in practice, the permeability is generally a function of the frequency. Mu-metal is a nickel-iron alloy (77% nickel, 15% iron, plus copper and molybdenum) that is very efficient for screening magnetic fields. ... Permalloy is a nickel iron alloy with about 20% iron and 80% nickel content. ... For other uses, see transformers. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ... The steel cable of a colliery winding tower. ... General Name, Symbol, Number nickel, Ni, 28 Chemical series transition metals Group, Period, Block 10, 4, d Appearance lustrous, metallic and silvery with a gold tinge Atomic mass 58. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Atomic mass 195. ... Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ... This article is about the chemistry of hydrogen. ... Look up Vacuum in Wiktionary, the free dictionary. ... Sapphire (from Hebrew: ספּיר Sapir) is the single-crystal form of aluminium oxide (Al2O3), a mineral known as corundum. ... General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance metallic pinkish red Atomic mass 63. ... Impact of a drop of water. ...


References

  1. ^ a b c d e "Relative Permeability", Hyperphysics
  2. ^ a b c Clarke, R. Magnetic properties of materials, surrey.ac.uk

See also


  Results from FactBites:
 
Permeability - Wikipedia, the free encyclopedia (131 words)
Permeability (electromagnetism), in electromagnetism, is the degree of magnetisation of a material in response to a magnetic field.
Permeability (geology) in geology, is a measure of the ability of a material to transmit fluids through it.
Vascular permeability, the movement of fluids and molecules between the vascular and extravascular compartments.
  More results at FactBites »


 
 

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