Definition of dielectric constant
Dielectric constant k (also called relative permittivity εr) is the ratio of the permittivity of a
substance to that of free space. A material containing polar components, such as polar
chemical bonds, which are presented as electric dipoles in Figure 2, has an elevated
dielectric constant, in which the electrical dipoles align under an external electric field. This
alignment of dipoles adds to the electric field. As a result, a capacitor with a dielectric
medium of higher k will hold more electric charge at the same applied voltage or, in other
words, its capacitance will be higher. The dipole formation is a result of electronic
polarization (displacement of electrons), distortion polarization (displacement of ions), or
orientation polarization (displacement of molecules) in an alternating electric field. These
phenomena have characteristic dependencies on the frequency of the alternating electric
field, giving rise to a change in the real and imaginary part of the dielectric constant
between the microwave, ultraviolet, and optical frequency range.