Abstract SCHIRACK, ANDRIANA VAIS. The Effect of Microwave ...

ε' = Relative real permittivity (dielectric constant)
ε" = Relative dielectric loss factor
j = Imaginary unit
The dielectric constant relates the ability of the material to absorb energy,
while the dielectric loss factor is related to various mechanisms of energy
dissipation. The dielectric loss is always positive and usually smaller than the
dielectric constant (Ryynanen, 1995). The dielectric constant decreases with
increasing temperature, while temperature has a variable effect on dielectric loss,
depending on the product. A large dielectric loss will translate into shorter heating
times (Giese, 1992).
Dielectric properties are most commonly measured in one of three ways: by
open-ended coaxial probe, transmission line, or by resonant cavity. In all of these
methods, a microwave signal is generated at a certain frequency and is directed at
or through the material being tested. By observing the changes in signal caused by
the material, the dielectric properties are calculated (Engelder and Buffler, 1991).
In general, food products have a loss factor of 25 or less, and exhibit a
penetration depth of 0.6-1.0 cm. However, dielectric properties change with the
composition of the food and with frequency. Both ε' and ε" are affected by the
moisture content, concentration of salt, frequency of electromagnetic field, and the
temperature. Dielectric properties are also affected by the physical state of the food.
For example, as the temperature of frozen goods rises through thawing, both ε' and
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