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Stan Zurek, Uniformity, Encyclopedia Magnetica,

Uniformity or homogeneity - a property of material1), field2), or in general distribution or another parameter3) such that the given quantity can be treated as uniform or not changing over the given region or range, either universally or under certain conditions. The variations might be present, but can be treated as negligibly small as far as the practical aspects of analysis are concerned.

Conversely, a non-uniform or non-homogeneous quantity changes are too significantly to be ignored.

Uniformity should not be confused with isotropy.

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Fig. 1. Distribution of magnetic flux inside a small air gap in the magnetic core is uniform, but non-uniform at the edges and outside of the gap
Fig. 2. Microscopically, materials used in powder cores are non-uniform, but macroscopically they can be treated as uniform (see also homogenisation)
Fig. 3. Laminated core is non-homogeneous locally, but from a global viewpoint it can be considered a volume with uniform magnetic properties laminated_core_-_magnetica.jpg

From practical viewpoint, at a macroscopic level many materials can be treated as uniform. For example large volumes of alloys, pure liquids or gasses display uniform properties, even though they can be anisotropic.

However, at sufficiently small scales the presence of atoms or elementary particles will always become noticeable.

Similar applies to intermediate levels, for structures either built all manufactured from smaller parts. Examples are shown in Fig. 2 and Fig. 3, where the structure non-uniform at a very local level, but the properties can be treated as homogeneous at the global level, due to averaging over the volume of interest.

Significance for magnetic measurements

Uniformity of magnetic field is a significant parameter in many magnetic measurements. Many magnetic phenomena are non-linear in their nature and thus reproducible measurements can be made only under well-controlled as well as uniform excitation conditions.

For example, several magnetic measurement standards IEC 60404 require that the sample is magnetised in an uniform way.4)5)6) Only then the required level of reproducibility can be attained between various apparatus and laboratories. The uniformity of magnetic field is such systems is achieved by an appropriate design of the sample under test and the magnetising yoke.

See also


uniformity.txt ยท Last modified: 2021/04/17 10:31 by stan_zurek

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