Dielectric Materials for Electrical Engineering

Chapter 1

Physics of Dielectrics 1

1.1. Definitions

A dielectric material is a more or less insulating material (with high resistivity and with a band gap of a few eV), that is polarizable, i.e. in which electrostatic dipoles exist or form under the influence of an electric field.

Like any material, it is an assembly of ions with positive and negative charges which balance, for a supposedly perfect solid, so as to ensure electrical neutrality. This neutrality is observed at the scale of the elementary structural motifs which constitute solids with ionocovalent bonding (ceramics, for example) and on the molecular scale in molecular solids (polymers and organic solids).

The action of an electric field at the level of these element constituent of solids manifests itself by dielectric polarization effects. Let us remember that the dipole moment of a charge q with respect to a fixed system of reference centered in O is:

[1.1]

where is the vector which connects the point O to the charge’s position.

If due to a force (caused, for example, by a magnetic field), the charge moves , then the variation of the moment will be:

[1.2]

represents the polarization effect of the field on the charge. ...