Utilizing microwaves for the determination of moisture content independent of density

Bulk density and moisture content are both very important powder-processing parameters that affect, among other things, the material's flowability and compressibility, as well as the final product's quality. Many traditional microwave methods to determine these parameters rely on the calculation of the real (ε′) and imaginary (ε″) components of the sample's relative complex permittivity. These parameters can also be calculated directly from raw sensor measurements. Using the conductance and frequency at resonance of an open-reflection microwave resonance sensor allowed the determination of a sample's moisture content (MC) with a high degree of accuracy. The method was applied to static samples of microcrystalline cellulose (MC range 0.568–6.163% and density range 0.280–0.499 g/cm3) and α-lactose monohydrate (MC range 5.59–8.69% and density range 0.346–0.691 g/cm3). The results indicated that the described method predicts moisture content accurately and independent of density fluctuations. As a result, the described method has been shown to be a viable alternative to other established microwave moisture content calibrations.

Comparison of MC determination residuals using the Translated Raw Variable, Meyer and Schilz, and the Trabelsi Universal Calibration methods on the same set of microcrystalline cellulose data.Figure optionsDownload as PowerPoint slide