# dielectric constant

Relative static permittivities of some materials at room temperature
Material Dielectric constant
Vacuum1 (by definition)
Air1.00054
Teflon™2.1
Polyethylene2.25
Polystyrene2.4–2.7
Paper3.5
Silicon dioxide3.7
Concrete4.5
Pyrex (glass)4.7 (3.7–10)
Rubber7
Diamond5.5–10
Salt3–15
Graphite10–15
Silicon11.68
Methanol30
Furfural42.0
Glycerol47–68
Water88–80.1–55.3–34.5
(0–20–100–200 °C)
Hydrofluoric acid83.6 (0 °C)
Formamide84.0 (20 °C)
Sulfuric acid84–100
(20–25 °C)
Hydrogen peroxide128 aq–60
(−30–25 °C)
Hydrocyanic acid158.0–2.3
(0–21 °C)
Titanium dioxide86–173
Strontium titanate310
Barium strontium titanate15 nc–500
Barium titanate90 nc–1250–10,000
(20–120 °C)
(La,Nb):(Zr,Ti)PbO3500,6000

The relative static permittivity (or static relative permittivity) of a material under given conditions is a measure of the extent to which it concentrates electrostatic lines of flux. It is the ratio of the amount of stored electrical energy when a potential is applied, relative to the permittivity of a vacuum. The relative static permittivity is the same as the relative permittivity evaluated for a frequency of zero.

The relative static permittivity is represented as εr or sometimes or K or Dk. It is defined as

where εs is the static permittivity of the material, and ε0 is vacuum permittivity. (The relative permittivity is the complex frequency-dependent , which gives the static relative permittivity for .)

Another term for the relative static permittivity is the dielectric constant, or the relative dielectric constant, or the static dielectric constant. These terms, while they remain very common, are ambiguous and have been deprecated by some standards organizations.[1][2] The reason for the potential ambiguity is twofold. First, some older authors used "dielectric constant" or "absolute dielectric constant" for the absolute permittivity rather than the relative permittivity.[3] Second, while in most modern usage "dielectric constant" refers to a relative permittivity[4], it may be either the static or the frequency-dependent relative permittivity depending on context.

By definition, the relative permittivity of vacuum, where , is equal to 1.

The static relative permittivity of a medium is related to its static electric susceptibility, by

in SI units.

## Measurement

The relative static permittivity εr can be measured for static electric fields as follows: first the capacitance of a test capacitor C0 is measured with vacuum between its plates. Then, using the same capacitor and distance between its plates the capacitance Cx with a dielectric between the plates is measured. The relative dielectric constant can be then calculated as

For time-varying electromagnetic fields, this quantity becomes frequency dependent and in general is called relative permittivity.

## Practical relevance

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. The layers beneath etched conductors in Printed Circuit Boards (PCBs) also act as dielectrics.

Dielectrics are used in RF transmission lines. In a coaxial cable, polyethylene can be used between the center conductor and outside shield. It can also be placed inside waveguides to form filters. Optical fibers are examples of dielectric waveguides. They consist of dielectric materials that are purposely doped with impurities so as to control the precise value of εr within the cross-section. This controls the refractive index of the material and therefore also the optical modes of transmission. However, in these cases it is technically the relative permittivity that matters, as they are not operated in the electrostatic limit.

## Chemical applications

The dielectric constant of a solvent is a relative measure of its polarity. For example, water (very polar) has a dielectric constant of 80.10 at 20 °C while n-hexane (very non-polar) has a dielectric constant of 1.89 at 20 °C.1 This information is of great value when designing separation, sample preparation and chromatography techniques in analytical chemistry.

## References

1. ^ Braslavsky, S.E. (2007), "Glossary of terms used in photochemistry (IUPAC] recommendations 2006)]", Pure and Applied Chemistry 79: p. 293-465; see p. 32, <[1]
2. ^ IEEE Standards Board (1997). IEEE Standard Definitions of Terms for Radio Wave Propagation p. 6.
3. ^ King, Ronold W. P. (1963). Fundamental Electromagnetic Theory. New York: Dover, p. 139.
4. ^ Jackson, John David (1998). Classical Electrodynamics, 3rd edition. New York: Wiley, p. 154.

1) D.R. Lide, Ed. CRC Handbook of Chemistry and Physics, 85th Ed. CRC Press. Boca Raton. 2004. pg. 8-141.

Room temperature (also referred to as ambient temperature) is a common term to denote a certain temperature within enclosed space at which human beings are accustomed.
A vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than standard atmospheric pressure. The Latin term in vacuo is used to describe an object as being in what would otherwise be a vacuum.
Air or Earth's atmosphere is a layer of gases surrounding the planet Earth.

Air may also refer to:
• Air (1977 video game), an air combat based mainframe computer game
• Air (band), a French electronic music duo

"Polythene" redirects here. For the Feeder album, see Polythene (album).

Polyethylene (IUPAC name polyethene) is a thermoplastic commodity heavily used in consumer products.
Polystyrene IPA: /ˌpɒliˈstaɪriːn/ is a polymer made from the monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry.
Paper is thin material used for writing upon, printing upon or packaging, produced by the amalgamation of fibres, typically vegetable fibers composed of cellulose, which are subsequently held together by hydrogen bonding.
silicon dioxide, also known as silica or silox (from the Latin "silex"), is the oxide of silicon, chemical formula SiO2, and has been known for its hardness since the 16th century.
Concrete is a construction material that consists of cement (commonly Portland cement) as well as other cementitious materials such as fly ash and slag cement, aggregate (generally a coarse aggregate such as gravel limestone or granite, plus a fine aggregate such as sand or

Pyrex is a brand name for heat-resistant glass introduced by Corning Incorporated in 1915.

## The name PYREX

A Corning executive gave the following account to Mitford M. Mathews (American Speech, Vol.
Natural rubber is an elastic hydrocarbon polymer that naturally occurs as a milky colloidal suspension, or latex, in the sap of some plants. It can also be synthesized. The entropy model of rubber was developed in 1934 by Werner Kuhn.
Diamond is an allotrope of carbon. It is the hardest known natural material and the third-hardest known material after aggregated diamond nanorods and ultrahard fullerite. Its hardness and high dispersion of light make it useful for industrial applications and jewelry.
Salt is a mineral essential for animal life, composed primarily of sodium chloride. Salt for human consumption is produced in different forms: unrefined salt (such as sea salt), refined salt (table salt), and iodized salt.
Graphite (named by Abraham Gottlob Werner in 1789 from the Greek γραφειν (graphein): "to draw/write", for its use in pencils) is one of the allotropes of carbon.
Silicon (IPA: /ˈsɪlɪkən/ or /ˈsɪlɪˌkɑn/, Latin: silicium
Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naptha or wood spirits, is a chemical compound with chemical formula CH3OH.
The chemical compound furfural is an industrial chemical derived from a variety of agricultural byproducts, including corncobs, oat and wheat bran, and sawdust. The name furfural comes from the Latin word furfur, meaning bran, referring to its usual source.
Glycerol is a chemical compound with the formula HOCH2CH(OH)CH2OH. This colorless, odorless, viscous liquid is widely used in pharmaceutical formulations.
Water is a common chemical substance that is essential to all known forms of life.[1] In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor.
Hydrofluoric Acid is a solution of hydrogen fluoride in water. Together with hydrogen fluoride, hydrofluoric acid is a valued source of fluorine, being the precursor to numerous pharmaceuticals, diverse polymers (e.g.
Formamide, also known as methanamide, is an amide derived from formic acid. It is a clear liquid which is miscible with water and has an ammonia-like odor. It is used primarily for manufacturing sulfa drugs and synthesizing vitamins and as a softener for paper and fiber.
Sulfuric (or sulphuric) acid, H2SO4, is a strong mineral acid. It is soluble in water at all concentrations. It was once known as oil of vitriol, coined by the 8th-century Arabian alchemist Jabir ibn Hayyan (Geber) after his discovery of the chemical.
Hydrogen peroxide (H2O2) is a very pale blue liquid which appears colourless in a dilute solution, slightly more viscous than water. It is a weak acid.
aqueous solution is a solution in which the solvent is water. It is usually shown in chemical equations as a subscript (aq). The word aqueous means pertaining to, related to, similar to, or dissolved in water.
Hydrogen cyanide is a chemical compound with chemical formula HCN. A solution of hydrogen cyanide in water is called hydrocyanic acid. Hydrogen cyanide is a colorless, very poisonous, and highly volatile liquid that boils slightly above room temperature at 26 °C (78.8 °F).
Titanium dioxide, also known as titanium(IV) oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO2. When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891.