A novel approach for dielectric constant measurement using microwave oscillators

In this paper, planar microwave oscillators are used to measure the dielectric constant of organic liquids for the first time. Dielectric constant of an unknown material is calculated based on the change in oscillation frequency caused by the material-under-test (MUT). A split-ring resonator (SRR) is chosen as the sensing element due its small area and high confinement of electric fields which makes it sensitive to permittivity changes of the MUT above the SRR. A C-band microwave oscillator prototype is fabricated on RT/Duroid 5880 substrate and calibrated using ethanol and methanol as reference materials. The dielectric constant of small quantities (<; 20μL) of acetic acid, xylene, isobutanol and ethyl acetate are extracted from measurement of oscillation frequency shift and show good agreement with previously reported values.