Dielectric behavior

Dielectric Material

Electrically insulating (non-metallic) material that exhibits or can be induced to exhibit an electric dipole structure. Commonly used in capacitors.

Electric Dipole Structure

Separation of positive and negative charges at the atomic or molecular level.

Electric Polarization

Alignment of electric dipoles along an applied electric field. This alignment is called polarization.

Polarization Types

• Electronic
  Displacement of the electron cloud relative to the nucleus. Occurs in all materials. Fast response, persists at high frequencies.
• Ionic
  Relative displacement of positive and negative ions in ionic solids. Slower than electronic polarization.
• Orientational
  Rotation of permanent dipoles (e.g. water molecules) to align with the field. Slowest. Only in materials with permanent dipoles.

Relative Permittivity

Here:

• $\epsilon$: permittivity of the material
• $\epsilon_0$: permittivity of free space ($8.85 \times 10^{-12}$ F/m)

$\epsilon_r$ is dimensionless. Also called the dielectric constant.

Dielectric Strength

Maximum electric field a dielectric can withstand before electrical breakdown (conduction). Units: V/m or kV/mm.

Capacitor Application

Inserting a dielectric increases capacitance by factor $\epsilon_r$:

Here $A$ is plate area and $d$ is plate separation.