Study On Soil Moisture Sensor Based On High-Frequency Electric Field

China is a large agricultural nation where water resources are extremely scarce and water consumption for agricultural production are large.The studies on monitor technique for soil water content are important to manage irrigation reasonably, to fine quantity irrigation, to save the fresh water resources, and to increase crop yield.In order to develop the technique to monitor on the water content in the soil, this paper briefly summarized the research state of soil water measuring techniques at home and abroad. It took the behavior of soil-water-system dielectrics as a key point. Through theoretical analysis on the behavior of soil-water-system dielectrics,it is proved that the dielectric constant can be used to measure soil water content rapidly.This method can get a lot of measurement results with high accuracy and wide applicability. In addition,the results are seldom affected by the spatial variation of soil property.Based on analyzing the operating principle of capacitive sensor,the investigating scheme for changing medium capacitivie sensor was determined,and soil moisture sensor based on high-frequency electric field was developed.We designed the structure of the probes based on the mathematical model of capacitive sensor and the hardware circuit of the sensor,and selected crystal oscillator as signal source.Meanwhile we designed detecting circuit with high-frequency diode,and micro control system based on AT89C51, which has the functions of data processing and result displaying.The experiment had shown the relationship between the frequency of signal source and water content.Took purple soil in Chongqing on approval,we find that different frequencies have a great effect on measurements of soil moisture content.And we choose 100MHz as the optimal test frequency for this capacitive sensor.To measure the soil water content by traditional oven drying method,and the corresponding output signal from the probes.Regressively analyzing the datum by applying least square so as to complete demarcating the sensor.The results indicated that the sensor has a good performance of accuracy,repeatability and stability,and can realize real-timely measuring soil humidity by testing its accuracy,repeatability and stability.