Measuring Frequency- And Temperature-Dependent Dielectric Properties of Food Materials

A technique employing an open-ended coaxial-line probe, network analyzer, and a sample temperature controldevice, designed for use with the coaxial-line probe, is described for measuring frequency- and temperature-dependentdielectric properties of food materials. Results of measurements on a macaroni and cheese food product are presented asan example at frequencies of 27, 40, 915, and 1800 MHz for the temperature range from 5 to 100C. Dielectric constantdecreases with increasing temperature, although more slowly in the 5 to 30C range at microwave frequencies of 915 and1800 MHz than at the lower dielectric heating frequencies of 27 and 40 MHz. The dielectric loss factor increases withincreasing temperature although it shows much less temperature dependence at the microwave frequencies.