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A dielectric is a nonconducting substance, i.e. an insulator. The term was coined by William Whewell^[1] in response to a request from Faraday. Whewell considered "dia-electric", from the Greek "dia" meaning "through", since an electric field passes through the material but felt that "dielectric" was easier to pronounce^{[citation needed]}. Although "dielectric" and "insulator" are generally considered synonymous, the term "dielectric" is more often used when considering the effect of alternating electric fields on the substance while "insulator" is more often used when the material is being used to withstand a high electric field^{[citation needed]}. Von Hippel, in his seminal book ^[2] takes this definition further. He states, Image File history File links Broom_icon. ... William Whewell In later life William Whewell (May 24, 1794 – March 6, 1866) was an English polymath, scientist, Anglican priest, philosopher, theologian, and historian of science. ...

"Dielectrics ... are not a narrow class of so-called insulators, but the broad expanse of nonmetals considered from the standpoint of their interaction with electric, magnetic, of electromagnetic fields. Thus we are concerned with gases as well as with liquids and solids, and with the storage of electric and magnetic energy as well as its dissipation."

Dielectrics is the study of dielectric materials and involves physical models to describe how an electric field behaves inside a material. It is characterised by how an electric field interacts with an atom and is therefore possible to approach from either a classical interpretation or a quantum one. In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field. ... Classical electrodynamics (or classical electromagnetism) is a theory of electromagnetism that was developed over the course of the 19th century, most prominently by James Clerk Maxwell. ... For a less technical and generally accessible introduction to the topic, see Introduction to quantum mechanics. ...

Many phenomena in electronics, solid state and optical physics can be described using the underlying assumptions of the dielectric model. This can mean that the same mathematical objects can go by many different names. This article is about the engineering discipline. ... Solid-state physics, the largest branch of condensed matter physics, is the study of rigid matter, or solids. ... For the book by Sir Isaac Newton, see Opticks. ...

Definitions

Electric field interaction with an atom under the classical dielectric model.

Classical

In the classical approach to the dielectric model, a material is made up of atoms. Each atom consists of a cloud of negative charge bound to and surrounding a positive point charge at its centre. Because of the comparatively huge distance between them, none of the atoms in the dielectric material interact with one another^{[citation needed]}. Note: Remember that the model is not attempting to say anything about the structure of matter. It is only trying to describe the interaction between an electric field and matter.^{[citation needed]}

In the presence of an electric field the charge cloud is distorted, as shown the top right of the figure. In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field. ...

This can be reduced to a simple dipole using the superposition principle. A dipole is characterized by its dipole moment, a vector quantity shown in the figure as the blue arrow labeled M. It is the relationship between the electric field and the dipole moment that gives rise to the behavior of the dielectric. Note: The dipole moment is shown to be pointing in the same direction as the electric field. This isn't always correct, but it is a major simplification, and it is suitable for many materials.^{[citation needed]} The Earths magnetic field, which is approximately a dipole. ... In linear algebra, the principle of superposition states that, for a linear system, a linear combination of solutions to the system is also a solution to the same linear system. ... In physics, the electric dipole moment is a measure of the polarity of a system of electric charges. ...

When the electric field is removed the atom returns to its original state.

Behavior

This is the essence of the model. The behavior of the dielectric now depends on the situation. The more complicated the situation the more rich the model has to be in order to accurately describe the behavior. Important questions are:

• Is the electric field constant or does it vary with time?
  • If the electric field does vary, does it vary quickly or slowly?
• What are the characteristics of the material?
  • Is the direction of the field important (isotropy)?
  • Is the material the same all the way through (homogeneous)?
  • Are there any boundaries/interfaces that have to be taken into account?
• Is the system linear or do nonlinearities have to be taken into account?

The relationship between the electric field E and the dipole moment M gives rise to the behavior of the dielectric, which, for a given material, can be characterized by the function F defined by the equation: . Isotropy (the opposite of anisotropy) is the property of being independent of direction. ... In physics, homogeneity is the quality of having all properties independent of the position. ... A linear system is a mathematical model of a system based on the use of a linear operator. ... In mathematics, a nonlinear system is a system which is not linear i. ...

When both the type of electric field and the type of material have been defined, one then chooses the simplest function F that correctly predicts the phenomena of interest. Examples of possible phenomena:

• Refractive index
• Group velocity dispersion
• Birefringence
• Self-focusing
• Harmonic generation

May be modeled by choosing a suitable function F. The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ... In optics, dispersion is a phenomenon that causes the separation of a wave into spectral components with different frequencies, due to a dependence of the waves speed on its frequency. ... A calcite crystal laid upon a paper with some letters showing the double refraction Birefringence, or double refraction, is the decomposition of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals, depending on... Rather than being dispersed, a beam of charged particles travelling in a gas environment sometimes becomes narrower. ... // Perturbative Harmonic Generation is a process where by laser light of frequency ω and photon energy ħω can be used to generate new frequencies of light. ...

Dielectric model applied to vacuum

From the definition it might seem strange to apply the dielectric model to a vacuum, however, it is both the simplest and the most accurate example of a dielectric.

Recall that the property which defines how a dieletric behaves is the relationship between the applied electric field and the induced dipole moment. For a vacuum the relationship is a real constant number. This constant is called the permitivity of free space, ε₀. In mathematics, the real numbers may be described informally as numbers that can be given by an infinite decimal representation, such as 2. ... Vacuum permittivity is the electric constant ε0 (also known as the permittivity of free space, or by the term dielectric constant of vacuum), which is a fundamental physical constant. ...

Applications

The use of a dielectric in a capacitor presents several advantages. The simplest of these is that the conducting plates can be placed very close to one another without risk of contact. Also, if subjected to a very high electric field, any substance will ionize and become a conductor. Dielectrics are more resistant to ionization than dry air, so a capacitor containing a dielectric can be subjected to a higher operating voltage. Layers of dielectric are commonly incorporated in manufactured capacitors to provide higher capacitance in a smaller space than capacitors using only air or a vacuum between their plates, and the term dielectric refers to this application as well as the insulation used in power and RF cables. See Capacitor (component) for a discussion of specific types. ... In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field. ... Ionization is the physical process of converting an atom or molecule into an ion by changing the difference between the number of protons and electrons. ... In science and engineering, conductors are materials that contain movable charges of electricity. ... Air redirects here. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... See Capacitor (component) for a discussion of specific types. ... Air redirects here. ... Look up Vacuum in Wiktionary, the free dictionary. ...

Some practical dielectrics

Dielectric materials can be solids, liquids, or gases. In addition, a high vacuum can also be a useful, lossless dielectric even though its relative dielectric constant is only unity.

Solid dielectrics are perhaps the most commonly used dielectrics in electrical engineering, and many solids are very good insulators. Some examples include porcelain, glass, and most plastics. Air, nitrogen and sulfur hexafluoride are the three most commonly used gaseous dielectrics. “Fine China” redirects here. ... This article is about the material. ... For other uses, see Plastic (disambiguation). ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... Sulfur hexafluoride is an inorganic compound with the formula SF6. ...

• Industrial coatings such as parylene provide a dielectric barrier between the substrate and its environment.
• Mineral oil is used extensively inside electrical transformers as a fluid dielectric and to assist in cooling. Dielectric fluids with higher dielectric constants, such as electrical grade castor oil, are often used in high voltage capacitors to help prevent corona discharge and increase capacitance.
• Because dielectrics resist the flow of electricity, the surface of a dielectric may retain stranded excess electrical charges. This may occur accidentally when the dielectric is rubbed (the triboelectric effect). This can be useful, as in a Van de Graaff generator or electrophorus, or it can be potentially destructive as in the case of electrostatic discharge.
• Specially processed dielectrics, called electrets(also known as ferroelectrics), may retain excess internal charge or "frozen in" polarization. Electrets have a semipermanent external electric field, and are the electrostatic equivalent to magnets. Electrets have numerous practical applications in the home and industry.
• Some dielectrics can generate a potential difference when subjected to mechanical stress, or change physical shape if an external voltage is applied across the material. This property is called piezoelectricity. Piezoelectric materials are another class of very useful dielectrics.
• Some ionic crystals and polymer dielectrics exhibit a spontaneous dipole moment which can be reversed by an externally applied electric field. This behavior is called the ferroelectric effect. These materials are analogous to the way ferromagnetic materials behave within an externally applied magnetic field. Ferroelectric materials often have very high dielectric constants, making them quite useful for capacitors.

An industrial coating is a paint or coating defined by its protective, rather than its aesthetic properties, although it can provide both. ... p-Xylene is an aromatic hydrocarbon, based on benzene with two methyl substituents. ... Mineral oil or liquid petrolatum is a by-product in the distillation of petroleum to produce gasoline. ... For other uses, see Transformer (disambiguation). ... The relative dielectric constant of a material under given conditions is a measure of the extent to which it concentrates electrostatic lines of flux. ... Castor oil is a vegetable oil obtained from the castor bean (technically castor seed as the castor plant, Ricinus communis, is not a member of the bean family). ... In electrical engineering High voltage refers to a voltage which is high. ... See Capacitor (component) for a discussion of specific types. ... In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor, which occurs when the potential gradient exceeds a certain value, in situations where sparking (also known as arcing) is not favoured. ... The triboelectric effect is a type of contact electrification in which certain materials become electrically charged after they come into contact with another different material and are then separated (such as through rubbing). ... Van de Graf generator. ... For the genus of fish family Electrophoridae, see electric eel An electrophorus is a single-plate capacitor used to produce imbalances of electric charge via the proces of electrostatic induction. ... Electrostatic discharge (ESD) is the sudden and momentary electric current that flows between two objects at different electrical potentials. ... Electret (formed of elektr- from electricity and -et from magnet) is material that has been permanently electrically charged (polarised). ... In physics, the ferroelectric effect is an electrical phenomenon whereby certain ionic crystals may exhibit a spontaneous dipole moment. ... Stress is a measure of force per unit area within a body. ... Piezoelectricity is the ability of some materials (notably crystals and certain ceramics) to generate an electric potential[1] in response to applied mechanical stress. ... For other uses, see Crystal (disambiguation). ... A polymer (from Greek: πολυ, polu, many; and μέρος, meros, part) is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ... In physics, the ferroelectric effect is an electrical phenomenon whereby certain ionic crystals may exhibit a spontaneous dipole moment. ... Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ...

See also

See Capacitor (component) for a discussion of specific types. ... In physics, the term dielectric strength has the following meanings: Of an insulating material, the maximum electric field strength that it can withstand intrinsically without breaking down, , without experiencing failure of its insulating properties. ... The relative dielectric constant of a material under given conditions is a measure of the extent to which it concentrates electrostatic lines of flux. ... A dielectric resonator is an electronic component that exhibits resonance for a narrow range of frequencies, generally in the microwave band. ... A dielectric permittivity spectrum over a wide range of frequencies. ... The electric susceptibility χe of a dielectric material is a measure of how easily it polarizes in response to an electric field. ... Dielectrophoresis (or DEP) is a phenomenon in which a force is exerted on a dielectric particle when it is subjected to a non-uniform electric field. ... A Low-K dielectric is one with a small dielectric constant. ... Permittivity is a physical quantity that describes how an electric field affects and is affected by a dielectric medium and is determined by the ability of a material to polarize in response to an applied electric field, and thereby to cancel, partially, the field inside the material. ... Vacuum permittivity is the electric constant ε0 (also known as the permittivity of free space, or by the term dielectric constant of vacuum), which is a fundamental physical constant. ... High K dielectric may be used in next generation electronic component to replace SiO2 Gate dielectric. ... Leakage describes an unwanted loss, or leak, of something which escapes from its proper location. ... Electret (formed of elektr- from electricity and -et from magnet) is material that has been permanently electrically charged (polarised). ... Piezoelectricity is the ability of some materials (notably crystals and certain ceramics) to generate an electric potential[1] in response to applied mechanical stress. ... In physics, the ferroelectric effect is an electrical phenomenon whereby certain ionic crystals may exhibit a spontaneous dipole moment. ...

References

1. ^ J. Daintith, "Biographical Encyclopedia of Scientists" CRC Press, 1994, ISBN 0750302879, page 943
2. ^ A. R. Von Hippel (ed), "Dielectric Materials and Applications", published jointly by the Technology Press of MIT and John Wiley, NY, 1954

External links

• Electromagnetism - a chapter from an online textbook
• Dielectric Sphere in an Electric Field