Editing Relative permittivity (section)

== Measurement ==
The relative static permittivity, ''ε''<sub>r</sub>, can be measured for static [[electric field]]s as follows: first the [[capacitance]] of a test [[capacitor]], ''C''<sub>0</sub>, is measured with vacuum between its plates. Then, using the same capacitor and distance between its plates, the capacitance ''C'' with a [[dielectric]] between the plates is measured. The relative permittivity can be then calculated as
: <math>\varepsilon_\text{r} = \frac{C}{C_0}.</math>

For time-variant [[electromagnetic field]]s, this quantity becomes [[frequency]]-dependent. An indirect technique to calculate ''ε''<sub>r</sub> is conversion of radio frequency [[S-parameter]] measurement results. A description of frequently used S-parameter conversions for determination of the frequency-dependent ''ε''<sub>r</sub> of dielectrics can be found in this bibliographic source.<ref>{{cite web|url=https://cdn.rohde-schwarz.com/pws/dl_downloads/dl_application/00aps_undefined/RAC-0607-0019_1_5E.pdf|title= Measurement of Dielectric Material Properties|first1=CheeYaw|last1=Kuek|publisher=R&S}}</ref> Alternatively, resonance based effects may be employed at fixed frequencies.<ref>{{Cite journal | last1 = Costa | first1 = F. | last2 = Amabile | first2 = C. | last3 = Monorchio | first3 = A. | last4 = Prati | first4 = E. | title = Waveguide Dielectric Permittivity Measurement Technique Based on Resonant FSS Filters | doi = 10.1109/LMWC.2011.2122303 | journal = IEEE Microwave and Wireless Components Letters | volume = 21 | issue = 5 | page = 273 | year = 2011 | s2cid = 34515302 | url = https://zenodo.org/record/894374 }}</ref>