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.