Dielectric Materials and Constants

As mentioned above, a dielectric is the middle layer between the two conductive plates of a capacitor and is generally composed of an electric insulation material such as a vacuum, non-ionized gas, solid such as a ceramic or polymer, or a liquid (aqueous or non-aqueous electrolyte). Two electrodes located at both sides of the dielectric collect the current. Since a dielectric is the primary material responsible for the storage of charge in capacitor devices, it exhibits extremely low conduction currents from free electrons and ion impurities. Although solids and liquids are predominantly used as insulators, vacuums and non-ionized gases are better insulators. 

There are two parameters used in characterizing dielectrics (1) leakage conductivity a, and (2) relative dielectric constant e,. The leakage conductivity is determined by the resistance of the material R (fl) thickness d (cm) and dielectric surface area A (cm ). Equation (1.16) expresses the leakage conductivity. 

The dielectric constant, also known as relative permittivity, can be defined. As described in Equation (1.1), if two charges and q 2 are separated from each other by a small distance r in a vacuum, the electrostatic force in vacuum (Fq) can be expressed as 

In the above equation, Sq is the electrical permittivity or dielectric constant of a vacuum. If the separation medium between the charges is replaced by another material. Equation (1.17) will become 

The relative dielectric constant of that material (s,) is found by dividing Equation (1.17) by Equation (1.18). 

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