Dielectric properties of corn flour from 0.2 to 10Â GHz

A modified form of existing geometrical set-up of sample holder and coaxial line probe which is coupled with Agilent E5071C vector network analyzer, is used to determine the dielectric constant ε′ and loss factor ε″ of corn flour at tapped densities 0.69, 0.63, 0.54 and 0.46 g/cm3 that correspond to moisture contents 8.8%, 12.6%, 17.4% and 22.7% wet basis respectively; and in the temperature and frequency ranges 25-75 °C and 0.2-10 GHz respectively. Measurements made at tapped density helps in designing microwave (MW) applicators as this density remains almost unchanged under unintentionally produced mechanical impacts, when flour is transported from grinding unit to applicators. Results show that ε′ decreases smoothly with increase in frequency at all temperatures and tapped densities, while ε″ decreases up to ∼1 GHz and then starts increasing. At a given frequency, change in both ε′ and ε″ with tapped density does not follow a particular trend for temperatures up to 50 °C; while increasing trend with decrease in tapped density is observed above 50 °C. Under strict controlled conditions such as power of electromagnetic field, exposure time, and desired maximum temperature of corn flour to get the acceptable quality of flour, these dielectric properties are beneficial to develop MW applicators for the purpose of thermal treatment to flour.