Author
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Nelson, Stuart |
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BARTLEY JR, PHILIP - OLD DOMINION UNIVERSITY |
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Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/30/2000 Publication Date: N/A Citation: N/A Interpretive Summary: Electrical characteristics of food materials, known as dielectric properties, are important because they influence the behavior of foods when exposed to electromagnetic fields for such purposes as heating or cooking in microwave ovens or in the industrial processing of foods by microwave or lower frequency dielectric heating for pasteurization, sterilization or other purposes. These properties, which determine how fas foods will heat in a microwave oven, need to be known, for example, in preparing dinners with different food products to be marketed to the consumer for final preparation in a microwave oven. Because the dielectric properties change as foods heat up, information about the variation of these properties with temperature is needed. Also, these properties vary with the frequency of the electric fields being applied to the food. Most domestic microwave ovens operate at a frequency of 2,450 MHz, but some industrial microwave processes use a frequency of 915 MHz, and some materials are better processed at lower frequencies of 27 and 40 MHz. This paper describes a technique for measuring the dielectric properties of a food sample as both temperature and frequency change over wide ranges of each. Results are presented for the dielectric constant and loss factor, two of the important dielectric properties, at frequencies of 27, 40, 915, and 1800 MHz for a macaroni and cheese product at temperatures from 0 to 100 degrees C (32 to 212 degrees F.) The technique offers a practical method for studying the dielectric properties of foods and will be useful to the food industry in providing better food products for the consumer. Technical Abstract: A technique employing an open-ended coaxial-line probe, network analyzer, and a sample temperature control device, designed for use with the coaxial-line probe, is described for measuring dielectric properties of food materials. Results of measurements on a macaroni and cheese food product are presented at frequencies of 27, 40, 915, and 1800 MHz for the temperature range from 0 to 100 degrees C. Dielectric constant decreases with increasing temperature, although more slowly in the 0- to 30-degree C range at microwave frequencies of 915 and 1800 MHz than at the lower dielectric heating frequencies of 27 and 40 MHz. The dielectric loss factor increases with increasing temperature although it shows much less temperature dependence at the microwave frequencies. |
