Nikolai Bukharin

The permittivity , or dielectric permittivity, is a physical property which describes the answer of a medium given to a Electric field. It is an essential size of the electrodynamic continuous mediums. It intervenes in many fields, in particular in the study of the propagation of the electromagnetic waves, and in particular the visible light. One thus finds it in Optique, via the Index of refraction. The laws managing the Refraction and the reflection of the light appeal there.

The permittivity is expressed in Farad S per meter (F/m). It can also be expressed by an adimensional quantity: the relative permittivity or permittivity, standardized compared to the Permittivity of the vacuum ε₀ = 8,854187×10^-12F/m: $\ epsilon = \ epsilon_0 * \ epsilon_R$

At the microscopic level, the permittivity is related to the electric Polarisabilité molecules or atoms constituting the medium.

The permittivity is a tensorial size (the answer of material can depend on the orientation of the crystallographic axes of material), which is reduced to a scalar in the isotropic mediums. It is very generally complex , the imaginary part being related to the phenomenon of absorption or emission of the electromagnetic field by material.

The permittivity is also noted K in the field of the integrated circuits and the semiconductors. The materials known as low-k are the dielectric ones with low permittivity. They are used as insulators between the metal interconnections to decrease the coupling between those.

Complex permittivity

In a real dielectric medium, there always exists with low frequencies a low conductivity related to various microscopic mechanisms (defects in particular). One then speaks about dielectric losses . One can take account of these losses by defining a complex permittivity:

$\ varepsilon (\ Omega) = \ varepsilon^ {\ premium} (\ Omega) - I \ varepsilon^ {\ premium \ premium} (\ Omega)$

These losses are often very weak. The imaginary part is thus very small in front of the real part. One speaks then sometimes about angle loss , expressed in pourcents and defined by:

$\ delta_e \ approx \ tan \ delta_e = \ frac {\ varepsilon^ {\ premium \ premium}} {\ varepsilon^ {\ premium}}$

This name is explained by the fact why this angle $\ delta_e$ is the angle formed by the vectors electric field and electric displacement in the complex plan.

The real and imaginary parts of the permittivity are not completely independent. They are connected by the relations of Kramers-Konig.

Relationships to other physical properties

Permittivity and susceptibility

Susceptibility

Permittivity and polarizability

The permittivity is a macroscopic size; polarizability is defined for an atom or a molecule. Under certain assumptions, it is possible to connect both: it is the formula of Clausius-Mossotti.

See too

External bonds

Constant dielectric of some materials (in)

Random links:

Ferrous ore-Quincey | Catharines saint | Hypodermic streaming | I am a cat | Jan Rubes