A miniaturized SIW circular cavity resonator for microfluidic sensing applications

This letter presents a miniaturized microfluidic sensor based on substrate integrated waveguide (SIW) cavity resonator. By choosing a circular cavity, a strong electric field is established in the center of the cavity, and the fluidic channel with sample under test is set up in the middle of the cavity for highly sensitive sensing. Several meander slots are loaded on the top of the cavity, which can extend the current flowing path and reduce the resonant frequency, thus the proposed structure is greatly miniaturized compared to the traditional resonators. The corresponding circuit model of the proposed sensor is derived and analyzed. Furthermore, the proposed sensor has been fabricated and tested. The water-ethanol mixture is used for verification. The measured results agree well with the simulated ones, and show that the sensor can distinguish different samples accurately. The resonant sensor works around 2.6 GHz, and shows very good sensitivity for permittivity change with miniaturized structure (0.31 × 0.29 × 0.0069 λ₀³). The sensor presents high sensitivity and excellent stability in a small size, which provide a novel solution to portable monitoring device.