Measurement of Complex Relative Permittivity of Pure Water and its Variation with Respect to Water Amount using Open-Ended Coaxial Probe

Abstract

A commercially available open-ended coaxial probe has often been used to measure dielectric properties in combination with a network-analyzer, while it can be applied to semi-infinite homogeneous materials. For thickness and size of the materials to be measured, however, their influences have not well been examined. In this study, using such an open-ended coaxial probe, we measured complex relative permittivity of pure water in the frequency range from 200MHz to 6GHz with respect to its measurement amount, and investigated the variation in comparison with the calculated values from an empirical formula for water permittivity. As a result, we found that the amount of water in a beaker with a diameter of over 35mm and a depth of 50mm provides the measurement variation within ±0.3% and -5.5% for real and imaginary parts of complex relative permittivity, respectively. It was also found that a water amount of 1.9ml in a beaker with a diameter of 35mm and a depth of over 2mm gives the variation within ±0.5% for real part and ±7% for imaginary part.