Double-sided parallel-strip line filter with an inserted conductor plane for solute concentration sensing

This study presents the design and implementation of a double-sided parallel-strip line (DSPSL) filter with an inserted conductor plane for the contactless detection of solute concentration in liquid solutions. Traditional methods of measuring concentration often involve direct interaction with a sample, which can lead to contamination. Conversely, the proposed DSPSL filter allows noninvasive measurements by placing the solution above the sensing side of the filter and this proposed filter is an insertion loss-based sensor. The design incorporates an inserted conductor plane that creates a 180° phase difference between the top and bottom networks, resulting in an effective band-stop filter configuration. When the concentration of the analyte decreases, the dielectric constant of the solution correspondingly increases, which affects the filter response. Furthermore, this study focuses on the filter's ability to detect varying concentrations of solutions, with a glucose solution as the experimental result, demonstrating notable frequency-shift responses when samples with concentrations ranging from 10% to 50% are loaded onto the sensor. The sensitivity of the DSPSL filter to changes in the dielectric properties indicates its potential for accurate concentration measurements. The results revealed a linear relationship between the dB(S₂₁) and the glucose concentration in the solution. A mathematical sensing model was also developed via regression analysis relating the glucose concentration to the measured dB(S₂₁) level. Copyright © 2025 IEEE.