Dielectric spectroscopy of wheat from 10 MHz to 1.8 GHz

Abstract

The dielectric properties (components of the complex permittivity relative to free space) of ground hard red winter wheat of 11–25% moisture content were determined by dielectric spectroscopy measurements with an open-ended coaxial-line probe and impedance analyser over the frequency range from 10 MHz to 1.8 GHz at temperatures from 5 to 95 °C. Both the dielectric constant and dielectric loss factor, over the stated range of variables, decreased with increasing frequency and increased with increasing moisture content and temperature. Plots of the dielectric constant and loss factor in the complex permittivity plane revealed a linear relationship between the two permittivity components at frequencies above 1 GHz, but they showed nonlinearity at lower frequencies due to the increasing influence of ionic conduction as confirmed by Cole–Cole plots of the permittivity data.