Dielectric Materials
AimsBefore you startIntroductionElectric dipolesPolarisation mechanismsCapacitorsThe dielectric constantVariation of the dielectric constant in alternating fieldsEffect of structure on the dielectric constantEffect of temperature on the dielectric constantLoss in dielectricsDielectric breakdownApplications of dielectricsSummaryQuestionsGoing furtherTLP creditsTLP contentsShow all contentViewing and downloading resourcesAbout the TLPsTerms of useFeedbackCredits Print this page
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Summary
- Dielectrics are electrical insulators that support charge.
- The properties of dielectrics are due to polarisation.
- There are three main mechanisms by which polarisation arises on the microscopic scale: electronic (distortion of the electron cloud in an atom), ionic (movement of ions) and orientational (rotation of permanent dipoles).
- A capacitor is a device that stores charge, usually with the aid of a dielectric material. Its capacitance is defined by Q = C V
- The dielectric constant κ indicates the ability of the dielectric to polarise. It can be defined as the ratio of the dielectric’s permittivity to the permittivity of a vacuum.
- Each of the polarisation mechanisms has a characteristic relaxation or resonance frequency. In an alternating field, at each of these (materials dependent) frequencies, the dielectric constant will sharply drop.
- The dielectric constant is also affected by structure, as this affects the ability of the material to polarise.
- Polar dielectrics show a decrease in the dielectric constant as temperature increases.
- Dielectric loss is the absorption of energy by movement of charges in an alternating field, and is particularly high around the relaxation and resonance frequencies of the polarisation mechanisms.
- Sufficiently high electric fields can cause a material to undergo dielectric breakdown and become conducting.