Dielektriseen

A dielectric is an insulating material that does not conduct electricity under normal conditions but can be polarized by an electric field. This polarization arises from the reorientation of molecular dipoles and the displacement of bound charges within the material, creating an internal field that opposes the external one.

Key properties include the permittivity, ε, and its relative form, the relative permittivity εr. The electric displacement D and the electric field E are related by D = ε0 εr E, where ε0 is the vacuum permittivity. In many applications, the capacitance of a structure increases when a dielectric fills a region between conductors: C = ε0 εr A/d for a parallel-plate geometry, where A is area and d is separation. The energy stored in a dielectric is U = 1/2 C V^2.

Dielectrics exhibit frequency-dependent behavior. The dielectric constant εr and the loss tangent tanδ vary with frequency, reflecting different polarization mechanisms: electronic, ionic, and orientation polarization. Polar dielectrics, which contain permanent dipoles, often show higher εr but stronger dispersion and loss.

Types of dielectrics range from nonpolar (low εr, low loss) such as air and many plastics, to polar (higher εr) liquids and solids. Ferroelectric materials display spontaneous polarization that can be reoriented by an external field, enabling nonvolatile capacitors and sensors.

Applications span capacitors, insulating layers in electronics, high-voltage cables, insulating oils, and various electromechanical devices such as piezoelectric actuators. Important considerations include dielectric strength, temperature dependence, moisture sensitivity, and long-term aging.