In-line microwave reflection measurement technique for determining moisture content of biomass material

An in-line microwave reflection measurement technique for determining moisture content of biomass material (sawdust) moving past the sensor on a conveyer is presented. The proposed system consists of four open-ended rectangular substrate-integrated waveguide (ORSIW) sensors mounted on the conveyor walls, three RF-switches and a 3.0 GHz six-port reflectometer for the reflection measurement from the sensors. The dielectric permittivity of the biomass as a function of moisture content and bulk density can be extracted by using the six-port measurement technique. The density-independent algorithm for moisture content determination was developed based on the power readings from the six-port circuit at conveyor speeds of 0.15, 0.23 and 0.35 m s−1. Finally, the predicted moisture contents were compared with those determined by the standard oven-drying method with standard errors of calibration (SEC) of 1.75%, 1.70% and 1.28% for conveyor speeds of 0.15, 0.23 and 0.35 m s−1, respectively.