In-Situ Monitoring of the Bulk Density and the Moisture Content of Rapidly Flowing Particulates Using a Microwave Resonance Sensor

The resonant frequency and conductance of an open-reflection microwave resonance sensor overlaid with rapidly stirring microcrystalline cellulose (moisture content range 0%-6.4% and effective bulk density range 0.225-0.375 g cm^-3) were recorded noninvasively in the frequency range of 700-740 MHz. With these data, empirical calibration models were developed that allowed simultaneous, accurate predictions of moisture content, and effective bulk density in-situ. Standard errors of calibration were found to be 0.32% for moisture content determination and 0.014 g cm^-3 for effective bulk density determination. This paper shows that microwave resonance sensors can be used to monitor the material properties of very rapidly flowing materials that other techniques cannot.