A low-cost microwave sensor based on open stepped impedance resonator for concentration and adulteration detection

Abstract A modified stop-band filter-based microwave sensor operating at 2.45 GHz within the license-free ISM band is presented for concentration and adulteration detection of liquid samples. The proposed sensor is implemented on a low-cost FR4 substrate and employs a compact resonant structure with direct-contact sensing capability. Experimental investigations demonstrate the capability of the sensor to accurately characterize high-loss materials, including ethanol, methanol, milk, and petrol solutions. The proposed design achieves an average sensitivity of 9.09 MHz ϵ ′ −1 with a normalized sensitivity of 0.37%, outperforming several recently reported microwave sensing structures. In addition, regression models developed from the measured scattering responses enable quantitative prediction of concentration levels and dielectric properties of unknown samples with an accuracy of approximately 96%. Owing to its compactness, low-cost implementation, and high detection capability, the proposed sensor is suitable for a wide range of microwave sensing and material characterization applications.