An Ultrahigh-Sensitivity Dual-Mode Microwave Sensor for Microfluidic Applications

In this letter, an ultrahigh sensitivity microwave microfluidic sensor is proposed to retrieve the dielectric properties of a liquid sample. Two metal strips in the ground plane defect are connected to the microstrip line through metallic vias. An interdigital capacitor (IDC) structure is introduced between the strips to produce a strong electric field confinement, so that the loaded liquid sample can fully interact with the field. The complex permittivity of the liquid sample affects the magnitude of the frequency offset and peak attenuation, thereby establishing a mathematical model for feature extraction of unknown liquid. The prototype of the proposed sensor is fabricated and measured. The experimental results show that compared with single-mode measurement, which only analyzes odd-mode frequency offset, dual-mode measurement can use frequency offset of odd- and even-mode to improve the sensitivity of the sensor by 43%.