High-Sensitivity Integrated Oscillator-Based Differential Microfluidic Sensor

This article presents a compact, high-sensitivity oscillator-based differential sensor, incorporating active circuits and a passive sensing network with interdigital capacitors (IDCs) and traveling-wave loop-directional filter for the first time. The IDC enables the electric field to be concentrated within a narrow area, facilitating micro liquid sensing with high sensitivity. Additionally, it also acts as a frequency selection network (FSN) for oscillator to enhance detection accuracy. The filter’s excellent matching, isolation, and distinctive pass/stop characteristics outside the resonant frequency contribute to differential sensing. The oscillation frequency of the microfluidic test channel varies with liquid’s permittivity, providing accurate differential sensing after mixing with the fixed reference channel frequency. Then the relationship between the liquid’s permittivity and differential frequency was established through curve fitting. Evaluation with a water-ethanol mixture demonstrates the sensor’s high sensitivity and error mitigation capabilities. In oscillator cases, the average sensitivity is 0.13% with a maximum error of 2.16%. Due to its differential structure, compact size, and high sensitivity, the proposed sensor holds significant practical value as an industrial organic chemical sensor. Furthermore, a local and remote synchronous sensing system based on this sensor is also presented.