Slide Presentations for ECE 329, Introduction to Electromagnetic Fields, to supplement “Elements of Engineering Electromagnetics, Sixth Edition” by Nannapaneni Narayana Rao Edward C. Jordan Professor of Electrical and Computer Engineering University of Illinois at Urbana-Champaign, Urbana, Illinois, USA Distinguished Amrita Professor of Engineering Amrita Vishwa Vidyapeetham, Coimbatore, Tamil Nadu, India

4.2 Dielectrics

Dielectrics are based upon the property of polarization, which is the phenomenon of the creation of electric dipoles within the material. Electronic polarization: (bound electrons are displaced to form a dipole) Dipole moment p = Qd

Orientational polarization: (Already existing dipoles are acted upon by a torque) Direction into the paper. Ionic polarization: (separation of positive and negative ions in molecules)

The phenomenon of polarization results in a polarization charge in the material which produces a secondary E.

Polarization Current

To take into account the effect of polarization, we define the displacement flux density vector, D, as vary with the material, implicitly taking into account the effect of polarization.

As an example, consider Then, inside the material,

D4.3 For 0 < z < d, (a)

(b) (c)

Isotropic Dielectrics: D is parallel to E for all E. Anisotropic Dielectrics: D is not parallel to E in general. Only for certain directions (or polarizations) of E is D parallel to E. These are known as characteristic polarizations.

D4.4 (a)

(b)

(c)