LAUSR

This letter presents a miniaturized differential microfluidic sensor by longitudinally integrating two substrate integrated waveguide (SIW) re-entrant cavity resonators (RECRs) for characterization of dielectric liquid materials. The mutual coupling between these two RECRs is prevented by the stacked metal wall between them. The feedline implemented by a microstrip-to-stripline-to-SIW transformer in the stacked metal wall is proposed to excite these two RECRs simultaneously. The dependence of complex permittivity of calibrated samples on the resonance frequency shift and quality factor of the sensor is used to build a predictive model of complex permittivity of liquid. The ability of this sensor to accurately measure liquid complex permittivity is verified by practical measurements.