Wheat stem moisture sensor using short probes based on SWR principle

A wheat stem moisture sensor was designed by standing wave ratio theory. The sensor probe has tow paralleled needles with 8 mm interval, which are 21 mm in length and 0.7 mm in diameter. Optimal length of the transmission line was 39 cm according to the experimental data. By comparing sensor output voltage and moisture content measured by oven drying method, we finally obtained the calibration equation for our wheat stem water content sensor. The sensor showed good stability, linearity and sensitivity, with a maximum deviation less than 3%, an average deviation of 1.126% and a standard deviation of 1.299%.