Nondestructive sensing of bulk density and moisture content in shelled peanuts from microwave permittivity measurements

Dielectric-based methods were used to determine nondestructively and simultaneously bulk density and moisture content in shelled peanuts from measurement of their relative complex permittivity at microwave frequencies (7–12 GHz) and 24 °C. The first method is based on direct relationships between the two components of the relative complex permittivity (dielectric constant and dielectric loss factor) and the bulk density and moisture content. The second method allows bulk density determination without knowledge of moisture content and temperature of shelled peanut samples from a complex-plane representation of the relative complex permittivity. Finally, moisture content in shelled peanuts is determined independent of bulk density changes with the use of density-independent permittivity functions. Statistical analysis provided bulk density and moisture content calibration equations at several microwave frequencies along with corresponding standard errors of calibration over wide ranges of bulk density and moisture content.