An SIW Oscillator for Microfluidic Lossy Medium Characterization

Microfluidic sensing is conventionally conducted using passive substrate integrated waveguides (SIW) due to high-Q performance. The proposed sensor, in this work, converts the very resonator (Qu ~ 600) at 3.17 GHz into oscillatory sensor utilizing negative feedback resistance. The phase noise is measured -143.4 dBc/Hz @ 1MHz with figure of merit of -203 dBc/Hz @ 1MHz. This active cavity with an embedded microfluidic channel is shown to preserve the sensitivity in calibration curve for common liquids and perform stably in sensing ultra-high salinity of 25% - 150 % in salt-in-water solutions.