Dielektromos

Dielektromos, in physics and electrical engineering, are insulating materials that can be polarized by an electric field but do not conduct sustained direct current. They reduce the effective electric field within the material and store electrical energy in the electric field, which is why they are essential in capacitors and insulation systems.

A central property of dielectrics is their permittivity, expressed as ε = ε0 εr, where ε0 is the vacuum permittivity and εr is the relative permittivity. The permittivity determines how much charge a given area and separation can store in a capacitor. Dielectrics also have a dielectric strength, the maximum electric field they can withstand before breakdown, and dielectric losses, which describe energy dissipation as heat. Dielectric behavior is often described by a complex permittivity ε* = ε' − iε'', or by the loss tangent tan δ. The apparent permittivity can depend on frequency and temperature, reflecting different polarization mechanisms.

Polarization in dielectrics occurs through several mechanisms: electronic, ionic, orientation (dipolar), and space-charge polarization. These processes respond on different time scales, so the dielectric constant can vary with frequency. On heating, molecular mobility changes, typically affecting both permittivity and breakdown strength.

Dielectrics are classified by composition into inorganic materials (ceramics, glasses), organic polymers, liquids, and gases (notably air). They may be further described as polar or nonpolar based on molecular structure and behavior in an electric field.

Applications include energy storage in capacitors, insulation in cables and high-voltage equipment, substrates and encapsulants in electronics, and dielectric resonators in RF and microwave devices. Common examples are air, glass, mica, polyethylene, polypropylene, ceramics like BaTiO3, and transformer oils.