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Diamagnets are materials with a magnetic permeability less than μ 0 (a relative permeability less than 1). Consequently, diamagnetism is a form of magnetism that a substance exhibits only in the presence of an externally applied magnetic field. It is generally a quite weak effect in most materials, although superconductors exhibit a strong effect.
The concept of permeability is of importance in determining the flow characteristics of hydrocarbons in oil and gas reservoirs, [4] and of groundwater in aquifers. [5]For a rock to be considered as an exploitable hydrocarbon reservoir without stimulation, its permeability must be greater than approximately 100 md (depending on the nature of the hydrocarbon – gas reservoirs with lower ...
Relative permeability, , for phase is then defined from =, as = / where is the permeability of the porous medium in single-phase flow, i.e., the absolute ...
To describe a soft ferromagnetic material for technical use, the following parameters are specified: (Relative) permeability Ratio of induction B in the material caused by some field H to an induction in a vacuum in the same field; it is a dimensionless value, as it is relative to a vacuum permeability;
Strip of permalloy. Permalloy is a nickel–iron magnetic alloy, with about 80% nickel and 20% iron content.Invented in 1914 by physicist Gustav Elmen at Bell Telephone Laboratories, [1] it is notable for its very high magnetic permeability, which makes it useful as a magnetic core material in electrical and electronic equipment, and also in magnetic shielding to block magnetic fields.
A closely related parameter is the permeability, which expresses the total magnetization of material and volume. The volume magnetic susceptibility , represented by the symbol χ v (often simply χ , sometimes χ m – magnetic, to distinguish from the electric susceptibility ), is defined in the International System of Units – in other ...
The typical relative permeability (μ r) of electrical steel is 4,000-38,000 times that of vacuum, compared to 1.003-1800 for stainless steel. [15] [16] [17] The magnetic properties of electrical steel are dependent on heat treatment, as increasing the average crystal size decreases the hysteresis loss.
The permeability of ferromagnetic materials is not constant, but depends on H. In saturable materials the relative permeability increases with H to a maximum, then as it approaches saturation inverts and decreases toward one. [2] [3] Different materials have different saturation levels.