Microwave moisture measurement of grains

Two independent, two-parameter techniques developed for online, in situ measurement of the bulk moisture content of grains using microwaves, are described. The first is noncontacting 4.9-GHz system configured so that a well-collimated TEM (transverse electromagnetic) beam is transmitted through a layer of grain, e.g., moving on a conveyer or flowing in a chute. The changes in attenuation and phase serve as two independent measurement parameters from which the wet and dry basis weights (g/cm²) and moisture can be found using a linear model, independent of the layer thickness. If the layer thickness is also known, the wet and dry densities (g/cm³) and complex dielectric constant can also be found. The second technique uses a contacting resonator sensor which can be conformably mounted or used as a portable probe. In this case the two independent measured parameters are the resonant frequency and the input mismatch (coupling) factor. Using an analytical model of the sensor, the complex dielectric constant of the grain is determined and then used to find the grain moisture content and density