Author
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Nelson, Stuart |
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Submitted to: Antennas & Propagation Society Symposium Digest Institute Electrical.......
Publication Type: Proceedings Publication Acceptance Date: 5/25/2005 Publication Date: 7/3/2005 Citation: Nelson, S.O. 2005. Dielectric spectroscopy studies on fresh fruits and vegetables. In: Proceedings of the IEEE Antennas and Propagation Society Digest. Session 148-8. CDROM. Interpretive Summary: There is a need for non-subjective determination of product quality in the handling of fresh fruits and vegetables. Ability to rapidly sense quality by use of intrinsic properties of the fruits and vegetables would be very helpful in the sorting and grading of these products for the market. Dielectric properties can be sensed with appropriate instruments that use electric fields for nondestructively probing the products. Radio-frequency dielectric properties of several fresh fruits and vegetable were measured and analyzed to provide background data for further research on this problem, and results of the research are reported in this paper. The variation of the dielectric properties of samples of apple, avocado, banana, cantaloupe, carrot, cucumber, grape, orange, and potato with frequency in the range from 10 to 1,800 MHz and with temperature over the range from 5 to 65 degrees Celsius was determined. The data provide interesting observations on the dielectric behavior of these fresh fruit and vegetable tissues, which determines how the tissues interact with electric fields that can be used to probe the quality of these products. Further studies are needed to learn whether these dielectric properties can be well related to quality factors, such as maturity, moisture content, and dry matter, which are properties of interest in working with many fruits and vegetables. Such future studies will determine whether the principles considered may be adapted to new instruments that can sense quality factors and provide advantages for producers handlers and consumers of these important agricultural products. Technical Abstract: The dielectric properties of nine fresh fruits and vegetables were measured over the frequency range from 10 to 1.8 GHz at temperatures from 5 degrees Celsius to 90 degrees Celsius. Both the dielectric constant and loss factor generally showed a monotonic decrease in value as frequency increased. At some frequency in the range between 10 and 120 MHz, the temperature dependence of the dielectric constant disappeared. At frequencies below this point, the templerature coefficient was positive, and above this frequency it was negative. Ionic conduction is most likely the dominant mechanism influencing the dielectric properties at the lower frequencies, and dipolar losses account for the behavior at the higher frequencies. In the range from 10 to 300 MHz and from 5 to 65 degrees Celsius, the log of the dielectric loss factor was expressed as a linear function of the log of frequency and temperature and could be modeled with a linear equaltion relating these three variables. |
