Tob. Sci., 1965, 9-26, p. 121-127, ISSN.0082-4523

Certain dielectric and physical properties of intact tobacco leaves

Harvesting and Farm Processing Research Branch, USDA, Agricultural Engineering Department, University of Kentucky, Lexington, Kentucky; and Agricultural Engineering Department, North Carolina State College, Raleigh, North Carolina USA

Dielectric measurements of tobacco indicated a broad frequency range over which dispersion of the dielectric constant occurred. A mathematical model for the dielectric behavior of the intact tobacco leaf was taken as a modified Debye model. By using the modified Debye model for expressing the dielectric constant and loss factor as a function of frequency, it was possible to predict the dielectric behavior outside the range of measurement. Measurements were made of the dielectric constant, dielectric loss factor, and specific conductivity of cured leaves as functions of frequency (1 kc to 1 mc), leaf moisture content (9-24 per cent), and density (0.500 to 1.000 g/cc) at a constant temperature of 77°F. The measurements were made on three well-known flue-cured varieties. Additional measurements were made on uncured leaves of one burley variety at 0.1 kc to 10 kc and at a moisture content of about 600% on the dry weight basis. The relatively high values of dielectric constant obtained for high-moisture samples indicated that the moist tobacco leaf was electrolytic in behavior. This was consistent with findings of other investigators [Tausz and Rumm, (14)]. The experimental results showed that increases in leaf moisture content increased the dielectric constant and dielectric loss factor, while frequency had the opposite effect. An increase in leaf density caused a proportionate increase in dielectric constant, but caused little change in the dielectric loss factor and a.c. conductivity. The high values of the dielectric properties for uncured leaves were assumed to be due to the higher moisture content; however, chemical content may account for some of the difference. The dielectric behavior of each of the six selections of flue-cured tobacco was similar within the limits of the experiment. In conclusion, for future work of a similar nature the arc plot of the real and imaginary components of the complex dielectric constant in an Argand diagram will enable one to make fewer measurements over a narrow band of frequencies in order to predict the dielectric parameters of biological materials.