ABSTRACT
Dielectric materials possess relatively few free charge carriers. Most of the charge carriers are bound and cannot participate in conduction. However, these bound charges can be displaced by applying an external electric field. In such cases, the atom or molecule forms an electric dipole that maintains an electric field. Complex permittivity of a material is determined using lumped circuits at low frequencies, and distributed circuits or free-space reflection and transmission of waves at high frequencies. Capacitance and dissipation factor of a lumped capacitor are measured using a bridge or a resonant circuit. The complex permittivity is calculated from these data. Propagation characteristics of electromagnetic waves are influenced by the complex permittivity of the medium. A parallel-plate capacitor is used to determine the complex permittivity of dielectric sheets. A cavity resonator can be used to determine the complex permittivity of materials at microwave frequencies.
