Risos A, Long N, Gouws G. A temperature compensated dielectric test cell for accurately measuring the complex permittivity of liquids.
THE REVIEW OF SCIENTIFIC INSTRUMENTS 2017;
88:105105. [PMID:
29092499 DOI:
10.1063/1.5005857]
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Abstract
A measurement of the complex permittivity, εr, of a liquid can give valuable information about the molecular polarizability and dielectric losses. This can be obtained by means of an impedance measurement using a parallel plate test cell. However, highly accurate and precise measurements are challenging, in particular when measuring as a function of temperature. Thermal expansion affects the geometry of a test cell and thus the measured capacitance from which εr is calculated. In this paper, a broadband four-terminal dielectric test cell is presented that is insensitive to temperature fluctuations. This was achieved by means of a cell geometry exploiting the thermal expansion coefficient of different materials. Experimental measurements on the manufactured cell yielded a stable capacitance of 35.322 ± 0.001 pF across 20 °C-90 °C. The capacitance stayed within ±0.01 pF over multiple experimental cycles of cleaning and assembly. A finite element modeling showed a theoretical accuracy in measuring εr better than 99.995%. The measured εr values for a number of standard liquids showed an agreement of 99.7% compared to literature values.
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