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Title: MICROWAVE DIELECTRIC STUDY OF BOUND WATER BEHAVIOR IN GRANULAR MATERIALS

Author
item TRABELSI, SAMIR - UNIVERSITY OF GEORGIA
item Nelson, Stuart

Submitted to: National Radio Science Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 6/5/2005
Publication Date: 7/3/2005
Citation: Trabelsi, S., Nelson, S.O. 2005. Microwave dielectric study of bound water behavior in granular materials [abstract]. URSI Digest, USNC/CNC/URSI North American National Radio Science Meeting, July 3-9, Washington, DC. Session 105-1. CDROM.

Interpretive Summary:

Technical Abstract: Granular materials are abundant in nature and many man made products are in granular form. One of the most important components of these materials is water. To accurately characterize these materials there is a need for a better understanding of water behavior. Water is sometime divided into two categories: free water and bound water. From an electrical standpoint, behavior of free water is well described by the Debye dielectric model with a single relaxation taking place at microwave frequencies, while little is known about the dielectric properties of bound water. They are described as lying somewhere between those of liquid water and those of ice depending on the degree of binding of the water molecules. In granular materials such as cereal grain and oilseed, bound water is expected to have several modes of binding depending on the inner structure of the kernels, the amount of water available, and the nature of surrounding molecules. One way to study bound water behavior is to examine changes in dielectric properties resulting from moisture and temperature changes. It has been observed, from measurements at microwave frequencies, on cereal grain and oilseed that effects of moisture content and temperature are interchangeable (Trabelsi et al., IEEE Transactions Instrumentation and Measurement, vol. 47, pp. 613-622, 1998). In this study, effects of both moisture and temperature are investigated independently for samples of wheat. Changes of water binding were tracked by tracking changes of microwave dielectric properties with time for wheat samples in which moisture content was suddenly increased to different moisture levels. Variations of dielectric properties of those samples at 10 GHz show that they decrease sharply and then reached a plateau and remained constant. For temperature investigation, samples of given bulk density and moisture content were cooled to –80 degrees Celsius, and their dielectric properties were measured as their temperature increased gradually to room temperature. Results at different microwave frequencies (between 5 GHz and 15 GHz) show that both the real part and imaginary part of the complex relative permittivity increase linearly with temperature and then increase faster with temperature beginning around –20 degrees Celsius. The slope change could be interpreted as a change in the nature of bound water behavior from tightly bound to more loosely bound.