Dielektrica

A dielectric, in physics and engineering, refers to an insulating material that does not conduct electric current under normal conditions but can be polarized by an applied electric field. Dielectrics are characterized by their permittivity, which measures how the material responds to the field. The absolute permittivity is written as ε = ε0 εr, where ε0 is the vacuum permittivity and εr is the relative permittivity or dielectric constant.

When a field is applied, microscopic dipoles align and bound charges shift, creating polarization. The polarization may arise from electronic, ionic, orientation, or interfacial mechanisms, and it depends on frequency and temperature. This response affects how the material stores and dissipates energy.

Dielectrics are primarily used for insulation and energy storage because of their high resistivity and finite dielectric strength, the maximum field a material can withstand before breakdown. They also exhibit dielectric losses, quantified by the loss tangent tan δ, which tends to increase with frequency and temperature and influences efficiency in AC applications.

Classification of dielectrics includes inorganic ceramics and glasses, organic polymers and fluids, and composite materials. They can be linear or nonlinear, isotropic or anisotropic, and some, such as ferroelectrics, exhibit spontaneous polarization. The choice of dielectric depends on properties like dielectric constant, breakdown strength, loss characteristics, and temperature stability.

Applications range from capacitors and electrical insulation in cables and devices to gate insulators in microelectronics and various sensors and actuators. The behavior of dielectrics in electric fields is described by Maxwell’s equations, with D = ε E describing the relation between electric displacement and the applied field, reflecting how bound charges modify field distribution.