Effective medium approximations

<p>In <a href="/facts/Materials_science/N5HrXRYW">materials science</a>, effective medium approximations (EMA) or effective medium theory (EMT) pertain to <a href="/facts/Computer_modeling/Re6o8vzN">analytical</a> or <a href="/facts/Scientific_theory/moMsLrUn">theoretical</a> modeling that describes the <a href="/facts/Macroscopic/NLwPDtLe">macroscopic</a> properties of <a href="/facts/Advanced_composite_materials_(engineering)/z8UVN8vB">composite materials</a>. EMAs or EMTs are developed from <a href="/facts/Averaging/etawWjw4">averaging</a> the multiple values of the constituents that directly make up the composite material. At the constituent level, the values of the materials vary and are <a href="/facts/Homogeneous/y84KQJxl">inhomogeneous</a>. Precise calculation of the many constituent values is nearly impossible. However, theories have been developed that can produce acceptable approximations which in turn describe useful parameters including the effective <a href="/facts/Permittivity/Sd3WtgT1">permittivity</a> and <a href="/facts/Permeability_(electromagnetism)/GA7CcRLU">permeability</a> of the materials as a whole. In this sense, effective medium approximations are descriptions of a medium (composite material) based on the properties and the relative fractions of its components and are derived from calculations, and effective medium theory. There are two widely used formulae.
</p><p>Effective permittivity and permeability are averaged dielectric and magnetic characteristics of a microinhomogeneous medium. They both were derived in <a href="/facts/Quasistatic_approximation/FfolWmBN">quasi-static approximation</a> when the <a href="/facts/Electric_field/tt4MooBs">electric field</a> inside a mixture particle may be considered as homogeneous. So, these formulae can not describe the particle size effect. Many attempts were undertaken to improve these formulae.
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Effective medium approximations