Miniaturized Quasi-Lumped Resonator for Dielectric Characterization of Liquid Mixtures

A novel miniature sensor operating at 150 MHz for real-time sensing of fluid concentrations is presented. The core of the sensor is a planar double-sided spiral split-ring resonator (DSS-SRR). At resonance, a strong electric field will be established mainly in the interdigital region of the DSS-SRR, producing a very sensitive area to a change in liquid concentration. A prototype is fabricated on RT/Duroid 5880 substrate and calibrated using deionized water/ethanol mixture. A mathematical model is derived to establish a relationship between resonance frequency and permittivity for sensor calibration. Good agreement has been reached between the actual and estimate values of permittivity. The proposed sensor offers other advantages, as high sensitivity, small sample volume, short assay time, low cost, and lab-on-a-chip compatibility. The major potentials are set in evidence from comparison with the state-of-the-art sensors.