A Wide Measured Range of Underground Soil Moisture Sensor Based on Resonance Frequency Method for Precision Agriculture

The precise soil moisture sensor is crucial for optimizing irrigation strategies and minimizing water wastage. Among various soil moisture sensor methods, frequency resonant-based sensor has emerged as the most suitable choice for cost-effectiveness and simplification. This study proposes a frequency resonant-based soil moisture sensor using an underground monopole antenna as a probe and a soil model. The very low reflection coefficient of the monopole antenna obtains the wide measured range of soil moisture levels up to 40%. The soil model is also investigated based on simulations and experiments to contribute to the accuracy enhancement. The proposed soil moisture sensor accuracy is evaluated from simulation to experiment with the root mean square error of 0.2869% and absolute error of 1.98% compared to the reference soil moisture level calculated from the water volume added.