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Chapter V Dielectric Study of ……
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Depending upon the frequency range under investigation the
experimental method of measuring dielectric constant varies. For frequencies
below 10 9 Hz the permittivity or impedance of a dielectric sample, inserted in
a parallel plate capacitor, can be measured by suitable circuits. A Schering
bridge arrangement is used up to 10 7 Hz and a resonance circuit is employed
in the range of 10 4 to 10 9 Hz. In the case of frequencies above 10 8 Hz, the
dielectric constant may be determined by measuring the interaction of
electromagnetic waves with the medium. From 10 8 to 10 11 Hz the material is
generally inserted in wave-guides or co-axial lines and the standing wave
patterns are measured. However at still higher frequencies, optical
techniques involving reflections and transmission measurements are
employed.
The applicability of dielectric materials not only requires the knowledge
of their electric properties, but also their general physical and chemical
properties, such as, mechanical strength, elasticity, resistance to heat and
cold, thermal conductivity, hygroscopic, stability, crystalline structure and
other parameters.
There are many applications of dielectric materials. Because the
dielectric constant is related to the chemical structure, it can be used for both
qualitative and quantitative analysis. If the dielectric constants for all
constituents except one constituent, in a multi-component system, are similar
and there is little interaction between them in solution, then the unique
component can often be determined. Interestingly, in the analysis for toluene
in the presence of complex mixtures of aliphatic hydrocarbons in petroleum
refining as well as determining moisture in cereal grains and other solids uses
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