A metal-ceramic coaxial cable Fabry-Pérot microwave interferometer for monitoring fluid dielectric constant

A metal-ceramic coaxial cable Fabry-Pérot interferometer (MCCC-FPI) has been developed as a new microwave sensor and demonstrated for fast and reliably measuring and continuously monitoring dielectric constants for pure and mixed liquids. The sensor only requires a simple reference scan of the interferogram for the FPI with its sensing chamber filled with air or under vacuum to determine the actual inter-reflector length. The sensor is validated by measuring room temperature dielectric constant (εr) at high frequencies around 1.4-4.7 GHz for three vegetable oils (corn, sesame, and olive), the synthetic Mobil®-1 engine oil, and mixtures containing sesame oil and water. The sensor has been also successfully demonstrated for determining εr values for the Mobil-1 oil at various temperatures and for the well-dispersed sesame oil-water mixtures of different compositions. The Bottcher's model of effective medium theory is shown to be better suited for predicting the εr of the sesame oil-water mixture than the Maxwell-Garnett and Bruggeman equations of spherical solutions.