VIAS Encyclopedia provides a collection of tables and definitions commonly needed in science and engineering.

## Dielectric Constant

Dielectrics are usually insulators. Examples include porcelain (ceramic), mica, glass, plastics, and the oxides of various metals. Some liquids and gases can serve as good dielectric materials, too. Dielectrics have the property of making space seem bigger or smaller than it is dimensionally. For example, when a dielectric material is placed between two electric charges it reduces the force acting between them, just as if they had moved apart. When an electromagnetic wave travels through a dielectric, the velocity of the wave will be slowed down and behave as if it had a shorter wavelength.

Electrically, the dielectric constant is a measure of the extent to which a substance concentrates the electrostatic lines of flux. More specifically it is the ratio of the amount of electrical energy stored in an insulator, when a static electric field is imposed across it, relative to vacuum (which has a dielectric constant of 1). Thus, the dielectric constant is also known as the static permittivity.

The dielectric constant εr is defined as the ratio:

εr = εs0

where εs is the static permittivity of the material in question, and ε0 is the vacuum permittivity. This permittivity of free space is derived from Maxwell's equations by relating the electric field intensity E to the electric flux density D. In vacuum (free space), the permittivity ε is just ε0, so the dielectric constant is 1.00.

The dielectric constant is an essential piece of information when designing capacitors, and in other circumstances where a material might be expected to introduce capacitance into a circuit. If a material with a high dielectric constant is placed in an electric field, the magnitude of that field will be measurably reduced within the volume of the dielectric. This fact is commonly used to increase the capacitance of a particular capacitor design

 Material Dielectric Constant Material Dielectric Constant air 1.00059 paraffin 2 to 3 aluminum silicate 5.3 to 5.5 plexiglass 3.4 bakelite 3.7 polyethylene 2.2 bees wax (yellow) 2.7 polystyrene 2.56 butyl rubber 2.4 porcelain 5 to 7 germanium 16 pyrex glass 4.6 glass 4 to 10 quartz 3.7 to 4.5 gutta-percha 2.6 silicone oil 2.5 halowax oil 4.8 steatite 5.3 to 6.5 kel-f 2.6 strontium titanate 233 lucite 2.8 teflon 2.1 mica 4 to 8 tenite 2.9 to 4.5 micarta 254 3.4 to 5.4 vacuum 1.00000 mylar 3.1 vaseline 2.16 neoprene rubber 6.7 water (distilled) 76.7 to 78.2 nylon 3.00 wood 1.2 to 2.1 paper 1.5 to 3

Last Update: 2010-12-14