Dielektrins

Dielektrins are insulating materials that do not conduct significant electric current under normal conditions but can be polarized by an external electric field. This polarization reduces the internal field relative to vacuum and enables energy storage, insulation, and control of electric fields in devices.

Key properties of dielectrics include the permittivity ε = ε0 ε_r, where ε_r is the relative permittivity (dielectric constant). ε_r depends on the material and frequency. Dielectrics also have dielectric strength, the maximum electric field before breakdown, and dielectric loss, often expressed as the dissipation factor tan δ, which reflects energy dissipation as heat. Polarization mechanisms—electronic, ionic, orientational, and interfacial—determine the frequency dependence of ε_r and tan δ.

Dielectrics are classified by phase into gases (for example, air), liquids (such as mineral oil or silicone oil), and solids (including ceramics, polymers, and composites). They are widely used in capacitors to increase capacitance, as insulating layers in cables and transformers, and as substrates in microwave and RF devices where ε_r and loss influence impedance and performance.

In linear, isotropic dielectrics, the electric displacement D and the electric field E are related by D = ε0 ε_r E, and the energy stored per volume is w = 1/2 ε0 ε_r E^2. The polarization P = ε0 (ε_r − 1) E. Dielectrics exhibit dispersion and relaxation, so ε_r and tan δ depend on frequency and temperature; models such as the Debye description capture some of these effects.

Reliability and safety concerns include dielectric breakdown under high field, partial discharges, moisture uptake, and aging, which can reduce ε_r and increase losses. Advances focus on low-loss polymers, high-ε_r ceramics, and composite materials for energy storage and high-voltage insulation.