Nondestructive and noncontact dielectric measurement methods for low-loss liquids using free space microwave measurement system in 8 - 12.5 GHz frequency range

Nondestructive, noncontact and real time evaluation of dielectric properties of low-loss liquids is important for applications such as service-aged transformer oil, biomedical, remote sensing and design of radar absorbing material. Free-space methods (which are nondestructive and noncontact) were developed for accurate measurement of dielectric properties of low-loss liquids at microwave frequencies. Two methods, namely, transmission only method and metal-back method are developed for measurements using a free space microwave measurement system (FSMM). The FSMM system consists of spot focusing horn lens antennas, mode transitions, coaxial cables and vector network analyzer (VNA). Dielectric constants and loss factors were measured for low-loss liquids such as dioxane, benzene and new transformer oil. It is observed that both the transmission only method and metal-back method are suitable for dielectric measurement of low-loss liquids.