dielectrice

A dielectric, in English, refers to an insulating material that can be polarized by an electric field. When placed in such a field, the internal charges shift slightly relative to one another, producing bound charges that oppose the field. This polarization reduces the effective field inside the material and enables the storage of electrical energy without conducting current.

Key properties of dielectrics include the relative permittivity (dielectric constant) ε_r, with the absolute permittivity given by ε = ε_r ε_0. Dielectrics also have a dielectric strength, describing the maximum electric field they can withstand before breakdown, and dielectric losses, which quantify energy dissipated as heat. Dielectrics often exhibit dependence on frequency and temperature, and may show nonlinear or hysteretic behavior in some materials.

In capacitors, inserting a dielectric between the plates increases capacitance by a factor equal to the dielectric constant: C = ε_r ε_0 A/d for a parallel-plate configuration. Dielectrics are also used for insulation in cables and transformers, as gate insulators in semiconductor devices, and in optical components where low loss and specific refractive indices are important.

Common dielectric materials include air or vacuum (reference standards), ceramics (for high-k applications), polymers such as polyethylene, polypropylene, and PTFE, glass, and composite or layered ceramics. Ferroelectric dielectrics exhibit large ε_r values and nonlinear polarization, useful for certain capacitors but with distinctive hysteresis.

Dielectrics can fail by electrical breakdown under excessive fields, moisture uptake, aging, or radiation effects. They are foundational to modern electronics, power systems, and photonics, enabling energy storage, insulation, and controlled electromagnetic propagation.