Editing Relative permittivity (section)

== Lossy medium ==
Again, similar as for [[lossy medium|absolute permittivity]], relative permittivity for lossy materials can be formulated as:
: <math> \varepsilon_\text{r} = \varepsilon_\text{r}' - \frac{i\sigma}{\omega\varepsilon_0}, </math>
in terms of a "dielectric conductivity" ''σ'' (units S/m, [[siemens (unit)|siemens]] per meter), which "sums over all the dissipative effects of the material; it may represent an actual [[Electrical conductivity|[electrical] conductivity]] caused by migrating charge carriers and it may also refer to an energy loss associated with the dispersion of ''ε''′ [the real-valued permittivity]" (<ref name=ChenVaradan2004/> p.&nbsp;8). Expanding the [[angular frequency]] {{nowrap|1=''ω'' = 2π''c''{{nnbsp}}/{{nnbsp}}''λ''}} and the [[electric constant]] {{nowrap|1=''ε''<sub>0</sub> = 1{{nnbsp}}/{{nnbsp}}''μ''<sub>0</sub>''c''<sup>2</sup>}}, which reduces to:
: <math> \varepsilon_\text{r} = \varepsilon_\text{r}' - i\sigma\lambda\kappa, </math>
where ''λ'' is the wavelength, ''c'' is the speed of light in vacuum and {{nowrap|1=''κ'' = ''μ''<sub>0</sub>''c''{{nnbsp}}/{{nnbsp}}2π}} = 59.95849&nbsp;Ω ≈ 60.0&nbsp;Ω is a newly introduced constant (units [[ohm]]s, or reciprocal [[siemens (unit)|siemens]], such that ''σλκ'' = ''ε''<sub>r</sub> remains unitless).