On impedance based RF dielectric sensors and applications in agricultural materials.

University of Minnesota M.S. thesis. August 2010. Major: Biosystems and Agricultural Engineering. Advisor: Dr. Jonathan Chaplin. 1 computer file (PDF); ix, 77 pages.Increasing numbers of commercially available sensors claim to use the dielectric response of grains and other agricultural materials to sense moisture and additional properties. A review of past and current research in this area gives a basis for investigating the efficacy and potential of one such instrument. A variety of materials, including corn, soybeans, wheat, ground feed, and soils were examined. Potential factors for varietal classification within and material type classification between samples was determined to be impractical due to the strong confounding effect of moisture dependence. Sensor electrode topology was briefly touched on, raising interesting questions about effects of geometry in dielectric sensors. The effect of material presentation was also evaluated for both static and flowing samples. Using continuously flowing samples, several varieties of corn were tested to evaluate existing density independent moisture functions and density functions. The results verified the effectiveness of many functions previously only studied in the microwave range for radio frequency instruments. In addition, a new density prediction function was discovered to have significantly better performance at radio frequencies