Highly Integrated Improved Hexagonal CSRR-Based Fluid Sensor for Complex Dielectric Parameter Detection

To enable rapid characterization of the complexpermittivity of unknown solutions, we propose a low-cost,compact, and highly integrated microwave microfluidic sen-sor. This sensor, fabricated on an FR4 substrate, employsa substrate-integrated waveguide (SIW) structure combinedwith a complementary split-ring resonator (CSRR). The struc-ture includes a ring of closely spaced metal vias surroundingthe hexagonal CSRR, enhancing the electric field's concen-tration. We optimized the sensor's parameters and developedits equivalent circuit model using ADS software. Interactionwith the sample occurs when a polydimethylsiloxane (PDMS)microfluidic channel, positioned above the sensing structure,contains the liquid sample. This setup alters the sensor's no-load frequency, initially set at 2.46 GHz, impacting the resonant frequency andQ-factor. We introduced a first-ordercharacteristic matrix model to analyze and confirm the sample's properties based on these changes. Our results, witha measurement error of approximately 5%, affirm the accuracy in determining the complex permittivity. The sensor'sdimensions are 44x30x0.8 mm(3), requiring a minimal sample volume of 2.32 mu L and offering a high sensitivity of 0.448%. Its ease of fabrication, capability for rapid noninvasive measurements, and high sensitivity make it an ideal toolfor noninvasive liquid characterization in biological and chemical fields