Gold Coplanar Waveguide Resonator Integrated With a Microfluidic Channel for Aqueous Dielectric Detection

This work presents the development of a coplanar waveguide based split ring resonator, integrated with a microfluidic channel suitable for liquid sensing applications. The sensor was fabricated via photolithography on a 0.5 mm borosilicate glass substrate with patterned gold. The microfluidic channel was aligned with the sensing area and bonded to the substrate to ensure consistent liquid volume (0.784 μL) over the sensing region. The microwave sensor was 1.5 × 3 cm
²
and had a resonant frequency between 19.3 and 19.4 GHz, offering the advantage of measuring extremely small sample volumes. The performance of the sensor was validated through simulations and a series of experiments using a |Z|-probe station. The sensor demonstrated a resonant amplitude sensitivity of -0.085 dB/vol.% for isopropyl alcohol in water (0-100 vol.%), 0.00023 dB/[mg/dL] for various glucose concentrations (50-1200 mg/dL), and 0.00056 dB/[mg/dL] for NaCl in water (50-1200 mg/dL, with equivalent Na+ 9226 mEq/L solutions); measured under room ambient conditions (24 ± 1
^o
C and RH: 36 ± 1 %).