MICROWAVE SOIL MOISTURE SENSOR BASED ON PHASE SHIFT METHOD AND INDEPENDENT OF ELECTRICAL CONDUCTIVITY OF THE SOIL

摘要

The present invention relates to soil moisture and soil matric potential measurement using microwave sensor composed of sensor element (1), porous matrix (2), phase shift measurement circuit (3) and circuit protective layer (4). Operating principle is based on the phase shift method in which phase shift of the signal propagating along sensor element (1) is related to the porous matrix (2) moisture content. Porous matrix (2) is in contact with surrounding soil (5) and reflects its water content. Phase shift measurement circuit (3) excite sensor element (1) and measures phase shift. The sensor is independent of soil electrical conductivity owing to the operating frequency in microwave range (~ GHz). In this manner, it is less sensitive to the soil type and therefore less demanding for calibration. The sensor is made of durable elements without consumable parts which enable a long-term operation. Its low power consumption makes it suitable for Internet of Things concept and automatic irrigation systems.