Editing Permittivity (section)

== Measurement ==
{{main|Dielectric spectroscopy}}

The relative permittivity of a material can be found by a variety of static electrical measurements. The complex permittivity is evaluated over a wide range of frequencies by using different variants of [[dielectric spectroscopy]], covering nearly 21 orders of magnitude from 10<sup>−6</sup> to 10<sup>15</sup> [[hertz]]. Also, by using [[cryostat]]s and ovens, the dielectric properties of a medium can be characterized over an array of temperatures. In order to study systems for such diverse excitation fields, a number of measurement setups are used, each adequate for a special frequency range.

Various microwave measurement techniques are outlined in Chen ''et al.''<ref name=Chen>{{cite book |first1 = Linfeng |last1 = Chen |first2=V. V. |last2 = Varadan |first3 = C. K. |last3 = Ong |first4 = Chye Poh |last4 = Neo |year = 2004 |chapter = Microwave theory and techniques for materials characterization |title = Microwave Electronics: Measurement and materials characterization |isbn=978-0-470-84492-2 |publisher=Wiley |page=37 |chapter-url=https://books.google.com/books?id=2oA3po4coUoC&pg=PA37 }}</ref> Typical errors for the [[Hakki–Coleman method]] employing a puck of material between conducting planes are about 0.3%.<ref name=Sebastian>{{cite book |first = Mailadil T. |last = Sebastian |year=2008 |title = Dielectric Materials for Wireless Communication |page = 19 |url=https://books.google.com/books?id=eShDR4_YyM8C&pg=PA19 |isbn=978-0-08-045330-9 |publisher=Elsevier}}</ref>
* Low-frequency [[time domain]] measurements ({{10^|−6}} to {{10^|+3}}&nbsp;Hz)
* Low-frequency [[frequency domain]] measurements ({{10^|−5}} to {{10^|+6}}&nbsp;Hz)
* Reflective coaxial methods ({{10^|+6}} to {{10^|+10}}&nbsp;Hz)
* Transmission coaxial method ({{10^|+8}} to {{10^|+11}}&nbsp;Hz)
* [[Quasi-optical]] methods ({{10^|+9}} to {{10^|+10}}&nbsp;Hz)
* [[Terahertz time-domain spectroscopy]] ({{10^|+11}} to {{10^|+13}}&nbsp;Hz)
* Fourier-transform methods ({{10^|+11}} to {{10^|+15}}&nbsp;Hz)

At infrared and optical frequencies, a common technique is [[ellipsometry]]. [[Dual polarisation interferometry]] is also used to measure the complex refractive index for very thin films at optical frequencies.

For the 3D measurement of dielectric tensors at optical frequency, Dielectric tensor tomography can be used.<ref>
{{cite journal
 |first1 = Seungwoo  |last1 = Shin   |first2 = Jonghee   |last2 = Eun
 |first3 = Sang Seok |last3 = Lee    |first4 = Changjae  |last4 = Lee
 |first5 = Herve  |last5 = Hugonnet  |first6 = Dong Ki   |last6 = Yoon
 |first7 = Shin-Hyun |last7 = Kim    |first8 = Joonwoo   |last8 = Jeong
 |first9 = YongKeun  |last9 = Park
 |display-authors = 6
 |year = 2022
 |title = Tomographic measurement of dielectric tensors at optical frequency
 |journal = [[Nature Materials]]
 |volume = 21  |issue = 3 |pages = 317–324
 |doi = 10.1038/s41563-022-01202-8
|bibcode = 2022NatMa..21..317S }}
</ref>