A Differential Measurement System for Liquid Dielectric Constant Optimized by SWTL

This paper presents an innovative differential measurement system for evaluating the dielectric constant of liquids, utilizing a planar microwave sensor combined with slow-wave transmission line (SWTL) for improving performance. The study first provides a detailed mechanism analysis of SWTL’s ability to enhance the resonance depth of sensors. Further, a high-Q-factor sensor design based on SWTL is developed to increase notch depth and reduce noise interference. The sensor operates at a center frequency of 1.5 GHz. To reduce the cost of measurement and the complexity of the test system, the sensor is integrated with a power divider and corresponding detection circuits, forming a self-contained differential architecture that enables standalone measurement without vector network analyzer (VNA). This integration provides a cost-effective and compact solution. Experimental results demonstrate that the system has high sensitivity of 1.19%, low mean relative error of 1.08%, and dielectric constant measurement with root mean square error of 2.10 and mean absolute error of 1.66%. Compared to the existing methods, the proposed system offers enhanced practicality and improves sensing performance through the combined use of SWTL-based sensor optimization and VNA-free differential signal processing, confirming its feasibility for practical applications in dielectric characterization.