Substrate-Integrated-Waveguide Based Microwave Differential Sensor with Additional Zero Point for Measuring Small Variations of Liquids

In this paper, we propose a microwave differential measurement sensor to detect the slight variations of the chemical and biological liquids' dielectric characteristic. The device consists of a power divider, two sensing branches and a hybrid. The sensing section on each branch is designed with substrate-integrated waveguide (SIW) technology and two eighth mode SIW(EMSIW) resonators with concentrated electric field tips are used to form a capacitive sensing gap. The sensitivity of the proposed sensor is enhanced at the differential zero point using the fast phase variation at its cut-off frequency. The self-resonance of the sensing branch introduces a new additional zero point. The two transmission zero points will shift simultaneously towards lower and higher frequencies respectively when different samples are loaded into microfluidic channel. The frequency difference between the two notches is used for the characterization of the liquid samples.