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: 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 unity. OVERVIEW
For time-varying electromagnetic fields, the dielectric constant of materials becomes Frequency dependent and in general is called Permittivity . PRACTICAL RELEVANCE The dielectric constant is an essential piece of information when designing Capacitor s, 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 Wiring Boards ( PWB s) 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 Waveguide s''. 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. Doped fiber can also be configured to form an Optical Amplifier . SEE ALSO |
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