MEASURING DIELECTRIC PROPERTIES OF HARD REDWINTER WHEAT FROM 1 TO 350 MHZ WITH A FLOW-THROUGH COAXIAL SAMPLE HOLDER

Abstract

A system for measuring the dielectric properties of cereal grains from 1 to 350 MHz with a coaxial sampleholder is presented. Several polar alcohols were used to calibrate and verify permittivity measurements obtained with asignal-flow graph model from the full two-port S-parameter measurements. At the lowest frequencies (1-25 MHz), wherethe phase measurements are less accurate, a lumped parameter model was used for the dielectric loss factormeasurements. The system was calibrated with measurements on air and decanol and verified with measurements onoctanol, hexanol, and pentanol. The standard error for the polar alcohols used for verification was 2.3% for the dielectricconstant and 7.6% for the dielectric loss factor. Although measurements were taken on static samples, the sample holderis designed to accommodate flowing grain. Dielectric properties measurements at 25C were taken on four hard redwinter wheat cultivars ranging in moisture content from about 9% to 21% with bulk densities varying from 0.66 to0.83 g/cm3. Most of the data agreed with measurements reported in the literature.