IMPROVEMENT OF THE DESIGN OF THE SENSING ELEMENT OF A CAPACITIVE SOIL MOISTURE SENSOR

Abstract

This work focuses on improving a capacitive soil moisture sensor to increase measurement accuracy and ensure stable performance under various operating conditions. The research is highly relevant due to the widespread use of such sensors in automatic irrigation systems, agriculture, and soil monitoring, where measurement reliability directly affects resource management efficiency and crop yields. Traditional moisture sensors have drawbacks related to soil heterogeneity. At high moisture levels, this can introduce nonlinearity into the sensor’s response due to a non-uniform distribution of the sensing volume, which ultimately reduces measurement accuracy. This paper proposes a design solution based on implementing a symmetrical configuration of the sensing element’s electrodes. The proposed symmetrical design significantly reduces the impact of the non-uniform distribution of the sensing volume within the measured medium and increases the sensing volume itself. This enhances the stability of the output signal and minimizes measurement errors caused by environmental changes. Furthermore, the expanded sensing volume increases the overall sensitivity of the soil moisture sensor. During the study, the sensing element design of an existing capacitive soil moisture sensor was analyzed. Computer modeling of the electrostatic field was performed to identify the primary source of error and justify the need for modernization. A new sensing element featuring a symmetrical coplanar capacitor was developed. Subsequent electrostatic field modeling and a comparative analysis between the existing and proposed sensing elements were conducted. Mathematical modeling confirmed that the proposed advanced design generates a symmetrical electrostatic field regardless of the medium. This allowed increasing the absolute sensitivity of the sensor by a factor of 1.65 (by 65.3 %) and ensuring a perfectly linear capacitance response. Specifically, the calculated reduced nonlinearity error decreased from 3.2 % (for the existing prototype) to 0.0 % across the entire measurement range (from completely dry soil to 100 % moisture). The practical significance of this work lies in the potential application of the developed sensing element in advanced soil moisture sensors. These sensors can be integrated into automatic soil moisture control systems, including smart irrigation networks and agricultural complexes. The proposed approach can be utilized in the further development of sensor technologies and the creation of more accurate and reliable measuring devices.