Planar non-contact microwave sensor for the detection of aqueous organic and inorganic samples

Abstract

In this study, a planar microwave sensor was proposed and manufactured with the aim of detecting and categorizing concentrations of various organic substances, including methanol (CH3OH), ethanol (CH3CH2OH), and 1-butanol (CH3CH2CH2CH2OH), as well as inorganic substances such as sodium carbonate (Na2CO3), potassium carbonate (K2CO3), and sodium hydroxide (NaOH). Throughout the sensor's development, a configuration incorporating a microstrip line and a rectangular patch with a central circular aperture was employed. Full-wave electromagnetic simulation software was utilized to analyze the performance of the sensor in terms of reflection coefficients. The sensor was fabricated using a PCB material with defined properties, which included a dielectric constant of 4.3, a loss tangent of 0.025, and a thickness of 1.6 mm. The reflection coefficient (S11) was measured and analyzed using principal component analysis (PCA) to identify correlations between the classification groups and concentrations of organic and inorganic samples. Additionally, the equivalent circuit has been extracted and modeled to describe the operating mechanism of the microwave sensor. The simulation and measurement results indicate that the sensor is a suitable candidate for the detection and classification of water samples containing CH3OH, CH3CH2OH, CH3CH2CH2CH2OH, Na2CO3, K2CO3, and NaOH. The proposed microwave sensor features a surface area of 29 × 18 mm², leading to a noteworthy reduction in surface utilization compared to other breath biosensors designed for measurement purposes.