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Abstract
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Accurate, low-cost measurement of volumetric water moisture (VWC) is needed for environmental monitoring and hydrology, yet many microwave methods require two-port fixtures or
invasive sampling. A compact one-port UHF sensor based on a short-circuited Goubau line (Gline) with complementary split-ring resonator (CSRR) loading is reported for soil moisture assessments. The sensing mechanism is absorption at a reflection-dip in reflection coefficient, whose resonant frequency shifts with soil permittivity. A dispersion analysis motivates operation in the 0.65–
0.75 GHz range, where temperature dependence of soil permittivity is moderate. The sensor is realized as a microstrip-fed G-line with a via short and CSRR inductive loading; measurements are
performed using a controlled sample holder. The method is validated on four soils (Ottawa sand,
bentonite, marl, and red clay), yielding linear regressions between the dip frequency F (MHz) and
volumetric water content (VWC, %) with R2 = 0.929–0.984. The sensitivity ranges from 1.81 to
2.19 MHz/%VWC, and the limit of detection (three-run repeatability, 3.3σ) is 0.21 %VWC. The
results demonstrate a traceable, one-port route to VWC estimation using a low-complexity G-line
probe suited to integration in environmental sensing systems.
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