Understanding Wave Impedance in Electromagnetics

This article explains the fundamentals of wave impedance in the context of electromagnetic (EM) wave propagation. As we know, when an electromagnetic wave propagates through a medium, a changing magnetic field (H) generates an electric field (E), and conversely.

The propagation of these waves is driven by these two oscillating H and E fields. The area closest to the source of radiation experiences a higher intensity of these fields.

Definition of Wave Impedance

Wave impedance is defined as the ratio of the electric field (E) to the magnetic field (H). Mathematically:

Wave impedance = |E| / |H|

Wave Impedance and Field Dominance

• High Wave Impedance: Wave impedance is high in regions where the electric field (E) is dominant. For example, this occurs with a straight wire fed by a high-impedance, voltage-driven source.
• Low Wave Impedance: Wave impedance is low in regions where the magnetic field (H) is dominant. This is observed in scenarios like a loop or coil fed by a low-impedance, current-driven source.