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

To enable rapid characterization of the complex permittivity of unknown solutions, we propose a low-cost, compact, and highly integrated microwave microfluidic sensor. This sensor, fabricated on an FR4 substrate, employs a substrate-integrated waveguide (SIW) structure combined with a complementary split-ring resonator (CSRR). The structure includes a ring of closely spaced metal vias surrounding the hexagonal CSRR, enhancing the electric field’s concentration. We optimized the sensor’s parameters and developed its equivalent circuit model using ADS software. Interaction with 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 and Q-factor. We introduced a first-order characteristic matrix model to analyze and confirm the sample’s properties based on these changes. Our results, with a measurement error of approximately 5%, affirm the accuracy in determining the complex permittivity. The sensor’s dimensions are
$44\times 30\times 0.8$
mm3, 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 tool for noninvasive liquid characterization in biological and chemical fields.