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 control device, designed for use with the coaxial-line probe, is described for measuring frequency- and temperature-dependent dielectric properties of food materials. Results of measurements on a macaroni and cheese food product are presented as an example at frequencies of 27, 40, 915, and 1800 MHz for the temperature range from 5 to 100 degreesC. Dielectric constant decreases with increasing temperature, although more slowly in the 5 to 30 degreesC 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.