Dual-Band Microwave Sensor for Sensing Application of Microfluidic Based on Transmission Line Loaded Pair of SIR Resonators

In this article, we propose two miniaturized dual-band microwave sensors for the sensing application of microfluidics. The two dual-band sensors are constructed by a microstrip line symmetrically and asymmetrically loaded with a pair of stepped impedance structure resonators (SIRs), respectively. To improve sensitivity and realize dual-band testing, the SIR with a long and thin split is selected. Different testing mechanisms are investigated for the symmetrical and asymmetrical sensors, respectively. In the symmetric condition (Sensor A), frequency splitting is used to measure different permittivity interferences of microfluidics. If only one SIR is substituted for its transpositional structure (Sensor B), the symmetry is broken. Then, field perturbation is used to test the permittivity interference of microfluidics. Certain simulations and experiments show that Sensor A has advantages over Sensor B, particularly for the small permittivity interferences. Some analyses are offered, including sensitivity, testing limitation, comparisons of two sensors, factors affecting the sensor’s sensitivity, and test uncertainty. For ethanol-water mixtures, the sensor can propose a maximum sensitivity of 62.74 MHz per 1% volume fraction. Experiments also show that the sensor can detect small changes in glucose-water mixtures between 0.02 and 0.025 g/dL with a maximum frequency shift of 4.4 MHz.