Characterization of Permittivity of Liquids-in-Flow with Spherical Dielectric Resonators

Several variants of dielectric resonator based setups are reported, which allow the measurement of complex permittivity of small amounts of liquids. A characteristic of the chosen spherical dielectric resonator is its mechanically simple connection to a planar feed circuit. The sensitivity of measurements is discussed with respect to the vectorial orientation of the electric fields, the permittivity and the volume of the sample liquid. Measurement results are reported for various liquids (water, methanol, ethanol, propan-2-ol) at frequencies around 5 GHz and at 70 GHz with small liquid quantities up to less than 10 nanoliters. The proposed measurement concept is shown to provide sensitive measurements at millimeter-wave frequency.