Using a Non-Foster Negative Capacitor to Increase Sensitivity of a Resonant Microwave Sensor for Permittivity Measurement of Liquids

A method to increase sensitivity of a resonant sensor for permittivity measurement is presented. The sensor is based on a quasi-lumped-element LC-tank whose resonant frequency is changed depending on permittivity of liquid filling a microfluidic canal between the capacitor electrodes. A non-Foster negative capacitor connected in series with the ordinary tank capacitor allows for broadening range of the tank resonant frequencies and increasing the slope parameter of the resonant frequency dependence on permittivity. Consequently, sensitivity of the sensor is increased that is of crucial importance to distinguish high-permittivity liquids from each other. An increase of the sensor sensitivity is demonstrated theoretically and by the results of electromagnetic simulations.