Microwave WGM Resonator with a Capillary Tube for the Characterization of Bioliquids

Abstract Microwave (MW) studies of biochemical liquids require the precise determination of permittivity and a convenient sample placement in a sterile channel, which must be cleaned or replaced after testing. These requirements can be effectively met using the MW characterization technique based on a high-quality whispering-gallery mode (WGM) quartz resonator with a capillary tube (CT) in a resonator hole filled with the liquid under test (LUT). A calibration approach based on simulations for the extraction of complex permittivity values of biochemical liquids of sub-microliter volumes was demonstrated and successfully verified. This was achieved through a special procedure for the analysis of the interaction of the electromagnetic field with the liquid in a CT inside a WGM quartz resonator and measurements of its frequency response. The reliability of the technique was validated by simulation and the measurement of liquids with known characteristics. The approach was successfully applied to obtain the complex permittivity of glucose in water solutions in the Ka-band.