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Abstract: This paper presents a bio-inspired slotted microstrip patch antenna (MPA) designed as a dual-parameter sensor for monitoring soil moisture and water salinity. The antenna employs a radiating patch patterned with spider-web-like and circular cross-shaped slots, which enhances its sensitivity to variations in the dielectric properties of materials placed in its near field. To enable contactless and non-destructive measurements, a hollow polydimethylsiloxane (PDMS) block is integrated above the patch and functions as a microfluidic chamber for sample analysis. The antenna’s performance was investigated using full-wave electromagnetic simulations in Ansys HFSS under two sensing conditions. For soil moisture, dry soil samples were gradually added with fresh water, increasing the volumetric water content (VWC) from 0% to 80%. In the second case, fresh water was mixed with salt concentrations ranging from 0.5% to 10% (w/v) to evaluate salinity response. The simulation results demonstrated strong sensing capabilities in both scenarios. For soil moisture detection, the antenna exhibited a consistent downward shift in resonant frequency as VWC increased, moving from 5.6 GHz in dry soil (0% moisture content) to 5.19 GHz at the 80% moisture content. For salinity detection, the reflection coefficient (S11) showed clear dependence on ion concentration, with the magnitude increasing from –17.48 dB at low salinity (0.5%) to –16.79 dB at high salinity (10%). This trend was attributed to conductivity-driven impedance mismatching in the water-salt mixtures. By associating frequency changes with soil moisture and S11 variations with salinity, the proposed antenna offers a compact and non-invasive solution for dual-parameter environmental sensing. Its bio-inspired slot structure and microfluidic chamber integration help to ensure high sensitivity and practical use. This novel design demonstrates the antenna's promise for low-cost and efficient monitoring systems in agriculture, irrigation management, and water quality testing.
Keywords: Bio-inspired, dual-parameter sensing, soil moisture and water salinity.
