A Novel Coplanar Capacitive Micro-Displacement Sensor Combining Microfluidic Channels for Bridge Health Monitoring

High-resolution micro-displacement detection plays a pivotal role in the realm of bridge health monitoring. Capacitive micro-displacement sensors stand out among contact measurement methods due to their high detection resolution but are limited by measurement range. This paper proposes a high-sensitivity and wide-range micro-displacement measurement technique by combining microfluidic system and planar interdigital capacitor performance optimization methods. Through analysis and simulation of the interdigitated electrodes (IDEs) sensor under diverse electrode configurations, the 8-pair electrode design can reach a peak sensitivity of 0.124 pF/mm across the 0 to 50 mm detection range with a resolution of 4 μm. To further boost the performance of the proposed microdisplacement measurement method, the integration of fractal structures into the electrode design has been explored, demonstrating a remarkable 1.5-fold sensitivity increase and a higher resolution of 2.6 μm compared to IDE-based sensors of identical order. Besides, we designed an S-shaped micro-channel deployed in areas with a strong electric field between electrodes, which has yielded an excellent linear response within a range of 0 to 4 mm and a nearly 2 times sensitivity enhancement. The research presented in this work may potentially contribute to the development of novel sensing methodologies for enhanced micro-displacement detection in bridge structures, ultimately leading to more accurate, efficient, and reliable structural health monitoring systems.