Relative Dielectric Permittivity

Relative Dielectric PermittivityRelative dielectric permittivity (or dielectric constant) of a medium ? is a dimensionless physical quantity characterizing the properties of an insulating (dielectric) medium. It is related to the effect of dielectrics polarization under the influence of an electric field.It shows in how many times the strength of electrostatic interaction in the medium is less than the interaction strength in vacuum. The relative permittivity of air and of the majority of other gases under normal conditions is close to unity (because of their low density). For most solid or liquid dielectrics relative permittivity ranges from 2 to 8 (for a static field).Dielectric constant of water in a static field is quite high, about 80. This value for substances with high electric dipole molecules is also quite high. The relative permittivity of ferroelectrics is tens or even hundreds of thousands.Relative permittivity ? of a substance can be determined by comparing the capacitance of a test capacitor with this dielectric and the capacitance of the same capacitor with vacuumDielectrics permittivity is one of the key parameters in development of electric capacitors. Using materials with high dielectric constant can significantly reduce the physical size of capacitors.Capacitance of a condenser is determined by the following formula:where ?r is dielectric constant of the material between the plates,?o is the electric constant, S is the area of the capacitor plates, d is the distance between them.The parameter of dielectric constant is taken into account when designing printed circuit boards. Dielectric constant of a material between the layers in combination with its thickness affects the static capacitance of voltage planes, as well as the wave impedance of conductors on the board.It should be noted that dielectric constant is strongly dependent on frequency of electromagnetic field. This fact should always be taken into account, as tables of reference books usually contain data for static fields or for low frequencies up to several kHz without indicating the fact.

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• capacitor
• capacity
• material
• physics