Submitted to: Digital Signal Processing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2005
Publication Date: 3/10/2006
Citation: Nigmatullin, R.R., Nelson, S.O. Fractional kinetics and dielectric relaxation in complex systems:dielectric properties of fresh fruits and vegetables from 0.01 to 1.8 ghz. 2006. Signal Processing 86:2744-2759. Interpretive Summary: Dielectric properties of materials are those electrical properties that influence the interaction of the materials with electromagnetic fields. For example, the dielectric properties of foods determine how rapidly they will be heated in a microwave oven. These properties can also be utilized with appropriate electronic instruments for sensing moisture content in grain, oilseed, and other agricultural products, because the moisture content is highly correlated with the dielectric properties of the materials. Dielectric spectroscopy is a means for measuring the dielectric properties of materials over a broad range of radio and microwave frequencies. Dielectric spectroscopy data measured on tissue samples from nine fresh fruits and vegetables (apple, avocado, banana, cantaloupe, carrot, cucumber, grape, orange, and potato) over the frequency range from 10 MHz to 1.8 GHz at temperatures from 5 to 95 degrees Celsius were furnished to a Russian theoretician for advanced mathematical analysis of their dielectric relaxation characteristics, which determine the dielectric properties of these materials. These analyses identified seven fitting parameters, which, when used with the mathematical relationships employed, provide excellent fitting of the curves for the dielectric properties. Further, the dielectric relaxation behavior of all of the tissues followed the same pattern, thus providing a new description of the dielectric relaxation processes in plant tissues. With further research, the dielectric properties fitting function may be useful in the application of dielectric spectroscopy for sensing quality factors such as maturity, which could then be used in the development of new instruments for nondestructive testing of fruit and vegetable products. Such new tools would be of value to growers, packers and processors in providing products of improved quality for consumers.
Technical Abstract: Based on the new theoretical approach and the self-consistent iteration procedure for calculating the limiting values of the frequency-dependent permittivity, it becomes possible to recognize the fitting function for the permittivity function measured for a complex system representing plant tissues of fresh fruits and vegetables in the frequency range from 10 MHz to 1.8 GHz. The recognized fitting function is common for all of a set of nine fruits and vegetables (apple, avocado, banana, cantaloupe, carrot, cucumber, grape, orange, and potato) and contains seven fitting parameters. These parameters are varied for different fruits and vegetables, and their behavior with respect to temperature is different but nevertheless exhibits some common features. This fitting function can be used for practical purposes to construct a desired calibration curve with respect to quality factors, as for example, moisture content or degree of maturity. The discovered common "universality" in dielectric behavior of such complex materials as plant tissues opens a possibility to use dielectric spectroscopy as a nondestructive method of control in analysis of electrical behavior (measured in the form of complex permittivity or impedance) for other complex materials.