Experimental study of a sensor for real-time measurement of soil moisture profile

A soil-moisture profile sensor with a sliding probe and an accessing tube was designed and tested based on the principle of the dielectric theory. Due to the limitation of Maxwell equations for modeling the electric-fringe distribution, this research was conducted as the following procedures:1) to determine the sensor's characterized parameters using a network analyzer and a variety of solvents with known relative electric constants; 2) to optimize the circuitry design with the identified electric parameters of the sensor; 3) to calibrate the sensor with different soil water contents under the laboratory conditions; 4) to validate the effect of the tube's thickness on the measurement results; 5) to perform a multi-layer test with a prepared soil column including three volumetric water contents. The statistic results of the measured data demonstrated a linear relationship between the normalized frequency shift of the sensor and soil volumetric water contents with a correlation coefficient of 0.95.