Optimization and evaluation of soil moisture sensor performance based on voltage value

Abstract Soil moisture content is a key parameter for agricultural water and fertilizer management as well as engineering safety assessment. Current sensing technologies often suffer from prohibitive costs, limited structural diversity, and high sensitivity to soil texture under complex conditions. To address these challenges, this study developed a voltage-based soil moisture measurement method employing an AC impedance voltage division strategy. Structural optimization and performance evaluations were conducted across three representative soils types: silt loam, sandy loam and clay loam. For these soils, 12 planar capacitive sensor configurations were designed and validated through controlled experiments covering a moisture range from 0% to 100%. Sensor output voltage was recorded in real-time to establish the relationship between soil moisture content and voltage, with performance evaluated based on response time, voltage sensitivity and voltage stability. The results indicate that the voltage based measurement method achieved coefficients of determination higher than 0.97 across all three soil types, demonstrating robust capture of moisture fluctuations. Annular electrodes, specifically A-2 and A-1, exhibited superior performance with shorter response times and higher voltage stability compared to rectangular variants, while R-2 performed particularly well in clay loam. This investigation confirms that electrode geometry governs signal amplitude and response characteristics by altering electric field distribution and effective sensing volume. With a unit cost of approximately USD 6.5 per sensor, representing a significant reduction from the USD 429 price point of typical commercial sensors, this design supports the large-scale deployment of low-cost, high-stability, and broadly applicable soil moisture content sensors.