A Microwave Sensor for Grain Moisture-Content Measurement Designed with Surface Wave Transmission Line

In this paper, a novel microwave sensor is presented to determine the moisture content (MC) of grains. The sensor is designed with microstrip surface wave launcher at 2.72 GHz and a single conductor transmission line. The grain sample is placed in a container between the launchers mounted on the conductor line. The experiments are performed with wheat samples of MC varying from 10% to 25%. Variation of $\mathrm{S}_{21}-$parameter (transmission coefficient) with MC at 2.72 GHz is recorded to be from -20.6dB to -45.2dB respectively, i.e., 1.64 dB attenuation per unit percentage MC value. The proposed sensor is compact, portable and can be used to accurately measure MC of the test samples in the field with the sensor and a portable VNA.