What is Dielectric Constant?

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- everything RF

Oct 6, 2018

The dielectric constant is the ratio of the permittivity of a substance to the permittivity of free space. It is dimensionless value and is also called relative permittivity.

Permittivity is the measure of a material's ability to store an electric field in the polarization of the medium i.e  it is a material property that affects the Coulomb force between two point charges in the material. The unit of permittivity is farad per meter (F/m).

Lets take the example of a capacitor for example - Let Co be the capacitance of the capacitor when air is filled between both its plates and let Cd be the capacitance of the same capacitor when a dielectric material is filled between the plates. Then, Dielectric Constant is given by the following:

Dielectric Constant is the ratio of capacitance of a capacitor filled with dielectric material to the capacitance of identical capacitor filled with air. The larger the dielectric constant, the more charge can be stored.

Dielectric Constant / Relative Permittivity of Various Substances

SubstanceDielectric Constant
Air 0˚C1.000594
Air 20˚C1.000528
Carbon Monoxide 25°C1.000634
Carbon Dioxide 25°C1.000904
Hydrogen 0°C1.000265
FR-4 (PCB material)4.8 typically
Paraffin wax2 - 2.4
Porcelain (Ceramic)2.2 - 2.36
PTFE (Teflon)2.1
Rubber2.0 - 2.3
Silicon Dioxide3.9
Calcium Titanate150
Strontium Titanate200