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Relative permeability must be between zero and one. In applications, relative permeability is often represented as a function of water saturation; however, owing to capillary hysteresis one often resorts to a function or curve measured under drainage and another measured under imbibition.
Magnetisation curve for ferromagnets (and ferrimagnets) and corresponding permeability. A good magnetic core material must have high permeability. [35] For passive magnetic levitation a relative permeability below 1 is needed (corresponding to a negative susceptibility). Permeability varies with a magnetic field.
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 ...
Craig [1] proposed three rules of thumb for interpretation of wettability from relative permeability curves. These rules are based on the value of interstitial water saturation, the water saturation at the crossover point of relative permeability curves (i.e., where relative permeabilities are equal to each other), and the normalized water permeability at residual oil saturation (i.e ...
Hysteresis loop Induction B as function of field strength H for H varying between H min and H max; for ferromagnetic material the B has different values for H going up and down, therefore a plot of the function forms a loop instead of a curve joining two points; for perminvar type materials, the loop is a "rectangle" (Domain Structure of Perminvar Having a Rectangular Hysteresis Loop, Williams ...
Saturation is most clearly seen in the magnetization curve (also called BH curve or hysteresis curve) of a substance, as a bending to the right of the curve (see graph at right). As the H field increases, the B field approaches a maximum value asymptotically , the saturation level for the substance.
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.
A practical unit for permeability is the darcy (d), or more commonly the millidarcy (md) (1 d ≈ 10 −12 m 2). The name honors the French Engineer Henry Darcy who first described the flow of water through sand filters for potable water supply. Permeability values for most materials commonly range typically from a fraction to several thousand ...