Electromagnetic impedance

Electromagnetic impedance
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Electromagnetic_impedance".

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In problems of electromagnetic wave propagation in a transmission medium, the electromagnetic impedance, also known as the intrinsic impedance, is defined as the ratio of the electric to magnetic field amplitudes:

$\eta = {E \over H}$

For a region with slight electrical conductivity ( $σ > 0$ , e.g. seawater), the equation becomes

$\eta = \sqrt{{j \omega\mu } \over {\sigma + j \omega \varepsilon} }$

where $ω$ is the frequency of the radiation, $μ$ is the permeability of the medium and $\varepsilon$ is the permittivity of the medium.

In a region with no conductivity ( $σ = 0$ , e.g. free space), the expression simplifies to

$\eta = \sqrt{\mu \over \varepsilon} \approx 377 \Omega$ (for a vacuum)

Electromagnetic impedance is not to be confused with electrical impedance.

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