A New Microwave Oscillator-Based Microfluidic Dielectric Sensor

This article proposes a novel microwave oscillator-based microfluidic sensor for measurement of the dielectric constant. The sensor consists of a sensing oscillator and a frequency demodulator. The sensing oscillator comprises a T-shaped $LC$ resonator (TLCR), which not only concentrates the electric field (E-field) in a narrow gap for liquid sensing but also serves as a frequency-selective element. When a test liquid is injected into the microfluidic channel placed above the sensing gap, the oscillation frequency of the sensing oscillator varies according to the liquid's dielectric constant, $\varepsilon{r}$. The proposed frequency demodulator converts this frequency-modulated (FM) signal into a corresponding voltage. Calibration liquids with known $\varepsilon{r}$ can be used to calibrate the microfluidic sensor and establish a relationship between the measured voltage and the dielectric constant. In this study, water-ethanol mixtures and water-glucose solutions are used as the test liquids to evaluate the measurement performance of the system. The measurements obtained using the proposed sensor agree very well with those obtained using a commercial dielectric probe. Since the proposed dielectric sensor has the advantages of high sensitivity, compact design, and a self-sustaining microwave test source, it has the potential to be further developed as a practical organic chemical sensor for industrial applications.