Tunable whispering-gallery-mode resonance sensor for the detection of dielectric loss of small volume liquid samples

In this paper, a tunable sensor with a decent dynamic range and a superior sensitivity for the detection of dielectric loss of liquid sample droplets in the millimeter-wave frequencies is proposed. The sensor works based on the whispering gallery mode resonances of a dielectric resonator which is coupled to a dielectric waveguide from the bottom. To extract the maximum dynamic range and sensitivity of the sensor, the coupling mechanism between the resonator and the dielectric waveguide has been designed to be controllable by using an adjustable screw. The border of the resonator is the most sensitive area of the sensor because of high interaction between the sample and the resonant fields of the resonator. Theoretical analysis and experimental verification for the proposed sensor are discussed.