Author
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Nelson, Stuart |
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KUANG, WENSHENG - UNIV GA DEPT AGRIC ENGR |
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Submitted to: Progress in Electromagnetics Research
Publication Type: Abstract Only Publication Acceptance Date: 7/7/1997 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: Dielectric properties of fresh fruits and vegetables are of interest for possible sensing of fruit and vegetable quality and for use in radio-frequency or microwave processing of such products. The microwave permittivities of 23 kinds of fresh fruits and vegetables were measured with an open-ended coaxial-line probe and network analyzer providing data for the frequency rate from 200 MHz to 20 GHz. Resulting curves showed a monotonic decrease in the dielectric constant with increasing frequency. The dielectric relaxations of the fruit and vegetable tissues were analyzed with the Debye equation and its derivatives. Cole-Cole plots and plots of the dielectric constant as a linear function of the product of angular frequency and loss factor, and also as a linear function of the quotient of the loss factor and angular frequency, revealed the frequency range from 2-20 GHz as appropriate for relaxation analysis. Thus, estimates of the relaxation frequencies, and the static dielectric constant, and high-frequency dielectric constant, were obtained for all the fruit and vegetable tissues. Relaxation frequencies generally ranged between 7-18 GHz, showing relatively broad distributions of relaxations for any given kind of fruit or vegetable. Static dielectric constants ranged between 45-75 with estimated high-frequency dielectric constants ranging between 7-24. Rough correlations were noted between the static dielectric constant and moisture content and between the relaxation frequency and total soluble solids, a measure of sweetness in fruits, but further studies on wider ranges of quality variables are needed to assess the usefulness of dielectric relaxation data for quality sensing in fruits and vegetables. |
