Microwave soil moisture sensor based on phase shift method and independet of electrical conductivity of the soil

Patent number: RS20180253 (A1) , RS60892

The present invention relates to the exact measurement of soil moisture which is of crucial importance in agriculture, since proper growth, development, and maintenance of the plants significantly depend on soil water content.

 

We have developed microwave soil moisture sensor based on phase shift method, which relies on the phase shift of a sinusoidal signal propagating along the sensor element which is heavily influenced by moisture content of the surrounding soil. The main advantages of the sensor originate from its operating principle and optimal operating frequency. Since the phase shift method measures phase and not the amplitude of the signal, the measurement results are more immune to the noise. By choosing optimal operating frequency in the microwave range, it is possible to neglect the influence of soil electrical conductivity. In this manner, it is achieved that the sensor is more independent from soil type in comparison to the state-of-the-art solutions and the need for its calibration is reduced.

 

The sensor is made of robust parts without consumable components, which enables its long-lasting operation with performances stable over time. Supporting electronics enables economical operation suitable for Internet of Things (IoT) concept, integration in wireless sensors networks as well as in systems for automatic irrigation.

 

The porous matrix within the sensor maintains hydrodynamic equilibrium with surrounding soil, thereby conveying a realistic state of the moisture content to the sensor element, and, at the same time, enabling excellent contact with the sensor element. By introduction of the relation between retention curve of the porous matrix and sensor output, it is possible the measure soil matric potential, which represents the best indicator of the water available to the plants. In addition, a temperature sensor is integrated within the soil moisture sensor leading to a hybrid solution offering measurement of three parameters, moisture, matric potential and temperature at the same time.