Traceable measurement of dielectric reference liquids over the temperature interval 10–50 °C using coaxial-line methods

A programme of measurement to establish traceable complex permittivity values for dielectric reference liquids at frequencies up to 5 GHz and at temperatures in the interval 10–50 °C has been completed and the results have been tabulated in a National Physical Laboratory Report (NPL Report MAT 23 , 2009). The liquids measured were high-purity methanol, ethanol, propan-1-ol, propan-2-ol, butan-1-ol, ethanediol and dimethyl sulfoxide. This paper describes the high-frequency coaxial cell measurement techniques that were used to obtain these data and the approach taken to uncertainty evaluation in this programme of work. Measurement results are summarized and compared with data from the scientific literature. Dielectric relaxation equations (Debye, double-Debye and Davidson–Cole) have been fitted to the data, to allow users to obtain best-fit values of complex permittivity at any frequency up to 5 GHz. A Monte Carlo modelling method has been used to evaluate permittivity uncertainties—this incorporates models of the behaviour of systematic measurement error. This uncertainty evaluation enables the dielectric data to be presented in a way that should maximize their utility.