# Permittivity Motivation: Dr. He's request from after the [[Shockley-Ramo Theorem| Shockley-Ramo test]], to differentiate between this and [[Resistivity]]. In electromagnetics, permittivity ($\varepsilon$) is one of the fundamental material parameters which affects the propagation of electric fields. Permittivity varies with a variety of parameters: frequency, temperature, and humidity, but for a majority of materials, this will be negligible. ==The permittivity is a measure of how much molecules of a given material oppose the external electric field.== Permittivity has units of [Farad/meter], and $\varepsilon_0 = 8.854 \times 10^{-12} F/m$ is the permittivity of free space, i.e. the permittivity of a vacuum. A material with low conductivity but a dielectric constant greater than 1 is a [[Dielectric Material]]. Some common permittivity values [^1] : | Material | $\varepsilon_r$ | |:-----------------------:|:---------------:| | Vacuum | 1.0 | | Air | 1.0006 | | Teflon | 2.1 | | Paper | 3.85 | | FR-4 | 4.0 | | [[CdZnTe (CZT) Detectors\| CdZnTe]] | ~10.9 [^2]| | Silicon | 11.7 | | Water (200 deg C) | 34.5 | | Water (20 deg C) | 80.1 | | Water (0 deg C) | 88 | | Calcium Copper Titanate | 250,000 | [^1]: https://maxwells-equations.com/materials/permittivity.php [^2]: [[@kitaguchiSpectralCalibrationModeling2011]]