Reference liquids for the calibration of dielectric sensors and measurement instruments

A comparative study of microwave complex dielectric permittivity data from different laboratories is provided for liquids. Four liquids—water, cyclohexane, methanol and dimethyl sulphoxide—are recommended as reference materials because their parameter sets from different measurements result in almost identical predictions of their dielectric properties in the frequency range up to 10 GHz. Within the limits of experimental error this agreement includes that of the extrapolated low frequency permittivity with the recently determined static permittivity of the liquids. Parameters for water are given for the frequency range 0–60 °C. For cyclohexane, which does not display relaxation behaviour up to the submillimetre frequency range, the frequency-independent permittivity is represented between 10 and 50 °C. Relaxation and static permittivity data for methanol and dimethyl sulphoxide are presented at 25 °C.