Dielektrisitet

Dielektrisitet, or dielectricity, is the property of insulating materials that allows them to be polarized by an electric field, thereby reducing the field inside the material and enabling electric field effects without sustained electrical conduction. Dielectrics are used for insulation, energy storage in capacitors, and various components in electrical and electronic systems. Their response to an applied field depends on frequency, temperature, and field strength.

A central parameter is the permittivity. The electric displacement D is related to the electric field E by D = ε0εrE, where ε0 is the vacuum permittivity and εr is the relative permittivity, or dielectric constant, of the material. The polarization P is given by P = D − ε0E. The capacitance of a capacitor with a dielectric between parallel plates is C = εA/d, with ε = ε0εr.

Dielectric behavior originates from several polarization mechanisms: electronic polarization of electron clouds, ionic polarization of bound ions, orientational polarization of permanent dipoles, and interfacial polarization at material inhomogeneities. These mechanisms affect εr and energy losses, described by the loss tangent tanδ. Dielectrics also have a dielectric strength, the maximum electric field they can withstand before breakdown, which can occur via various mechanisms such as avalanche or thermal breakdown.

Applications include electrical insulation in cables, motors, and transformers, as well as energy storage in capacitors and as gate insulators in semiconductors. Dielectrics are chosen for high permittivity combined with low losses and high breakdown strength, and their properties are often temperature- and frequency-dependent.