Radio Frequency Microfluidic Dielectric Sensor With Self-Injection-Locked Technology

A new radio frequency (RF) microfluidic dielectric sensor with self-injection-locked (SIL) technology is proposed in this article. A SIL sensor mainly consists of a microfluidic sensing structure and an injection-locked oscillator (ILO). On top of this configuration, a dielectric sensor can be implemented by integrating a frequency demodulator. When the microfluidic channel is loaded with liquids of different concentrations, the SIL sensor outputs the signals with frequencies corresponding to these concentration levels. Then, the frequency demodulator transforms the output signals into the corresponding dc voltages V-o . By means of nonlinear regression analysis, a third-order polynomial equation can be derived to relate V-o to the reference dielectric constant, epsilon(r,ref), for the sensor calibration. In this study, 7.5-mu L water-ethanol mixtures with ethanol volume fractions (EVFs) of 20%-80% in increments of 20% are used as the test liquids to evaluate the proposed dielectric sensor. Compared to the results obtained using a commercial dielectric probe, the maximum error of epsilon(r,meas) measured using the proposed dielectric sensor is found to be 4.39%. Because the proposed dielectric sensor has a simple architecture, a compact design, and an autonomous RF test source, it has the potential to be developed as an organic chemical sensor for use in biomedical applications.