Characterization and modeling of a relative permittivity sensor for liquids

The relative permittivity sensor is a newly developed chip from the Micro-Mechanical-Electrical Systems (MEMS) group at the University of Twente. The MEMS group has designed and fabricated the chip to measure the relative permittivity of the fluids continuously flowing through the chip. The newly developed chip has multiple sensors with different electrode setups integrated into the microfluidic channels. The voltage over the electrodes can then be measured; using the capacitance equation, the relative permittivity of the fluid can be calculated. This paper focuses on the characterization and modeling of the three designs: comb structure, wall plates, and channel plates. Each sensor was tested for accuracy and reliability for four different materials. The methodology includes the electric model, analysis of the sensors, and correlating the measured signals to the relative permittivity of the fluids. The result indicates that all sensors need further investigation. The channel plates showed an average accuracy of 45% error, and the comb structure showed the expected behavior but with a noticeable deviation from the expected values In contrast, the wall plates showed unanticipated behavior.