Dielectric

As a dielectric (plural: dielectrics) is refers to any electrically weak or non-conductive, non-metallic substance, the charge carriers are generally not free to move. A dielectric can be a gas, a liquid or a solid.

Operates, for example, around a cable, an electric field, the term dielectric can be used for the space in which this electric field is effective to be used. A dielectric is therefore one of a finite electric field, spatial location ( from the Greek dia, " through ", that is, the field goes through the material ). There may not remain no electrical conductivity present in this room. Dielectrics may be present in empty space ( vacuum) in the gas-filled room or other, filled by electrically non-conductive material volume.

The field sizes of the dielectric, the electric field strength E and the electric flux density D, which in the electrostatic case, i.e. in the case of time-constant, and are combined in an isotropic medium of the permittivity on the following relationship:

The permittivity is composed of the electric field constant and the material-specific relative permittivity:

Term use

Insulators, as insulating material between the capacitor plates, coaxial cables and the like. are referred to as dielectric. Also antennas may have function-determining dielectric devices.

Furthermore, the liquid of an electric discharge machine, which prevents the spark of the electrode is too long, referred to as dielectric.

Insulation materials that serve each other only for electrical insulation, conductive parts are not usually referred to as dielectrics, although their dielectric properties can be crucial for their functioning.

Polarization of a dielectric

Since the charge carriers are not free to move in a dielectric, they are polarized by an external electric field. Here, the polarization is made between two types:

Dielectrics in capacitors

The capacitance of a capacitor essentially depends on the dielectric used and the relative permittivity of the electrode area A and the distance of the electrodes from each other.

For a plate capacitor holds:

The higher the relative permittivity is, the more energy can be stored in the electric field between the plates of a capacitor. The relative permittivity of the insulating material selected states, therefore, to the which the capacitance of a capacitor with respect to vacuum (or air ) increases as an insulating material.

An important parameter of a dielectric in capacitors and cables is also its dielectric strength, that is, at what voltage the dielectric loses its insulating properties and it comes to rollovers between the capacitor plates.

Depending on the application, the dielectric loss factor at capacitor dielectrics plays a role. He leads with AC voltage to the heating of the capacitor. The marked for some materials dielectric absorption can lead to a partial recharging of a capacitor after a complete discharge by short circuiting.

Dielectrics in cables, high-frequency and high-voltage components,

Dielectric also referred to the insulating material between the conductors of a cable (especially high- frequency and coaxial cables ), which essentially determines the characteristic impedance and the frequency-dependent attenuation per length (usually expressed in decibels [dB ] or Neper [ Np ] per km).

Dielectric antennas, resonators and dielectric waveguides are used in radio-frequency engineering and obey the same laws here as the refractive in the optics or with light guide cables.

Typical dielectric materials in high frequency applications are polyethylene, PTFE, ceramic (e.g., steatite, aluminum oxide), mica or air.

Dielectrics for high frequency applications must generally have very low dielectric dissipation factors.

The same is true for example for high voltage components such as cables or transformers. Here is the dielectric primarily from the oil-soaked paper insulation between the cable conductor and shield, or between the transformer windings. The dielectric properties of these components can for example provide information about the quality of the insulation.