A New Design of Soil Moisture Sensor Based on Frequency Domain Reflectometry

A new design of soil moisture sensor using frequency domain reflectometry technology is introduced by derivation of equation of high frequency response of transmission line.With proper length of transmission line and appropriate resonance circuit,a simple comparator circuit connected in parallel to the resonance circuit with standing wave can determine the relationship between signal frequency and relative permittivity of soil.Thus soil moisture can be calculated in theory of permittivity and ingredient of soil.The structure of new sensor is presented and data measured is shown.Results show that data from the new sensor matches that from oven drying method,and the maximum error is less than 2%,which can meet the need of agrometeorological monitor.