To develop advanced drying methods based on microwave (MW) and radio frequency (RF)
heating, knowledge of dielectric properties is essential for understanding the interaction
between electromagnetic fields and peanuts. In this study, dielectric properties of peanut
kernels were measured between 10 and 4500 MHz using an open-ended coaxial-line probe
and network analyser at temperatures between 25 and 85 C and moisture contents between
10% and 30% on a wet basis (w.b.). The results showed that both dielectric constant
and loss factor of peanut kernels decreased sharply with increasing frequency over RF
range (10e300 MHz), but gradually over the MW range (300e4500 MHz). Both dielectric
constant and loss factor increased with increasing moisture content and temperature. The
rate of increase was greater at higher temperature and moisture levels than at their lower
levels. Penetration depth decreased with increasing frequency, moisture constant, and
temperature. The measured dielectric properties were finally applied to determine the
temperature profiles of RF heated samples under three moisture levels using experiment
and simulation. This study on dielectric properties may provide useful guidelines in
developing effective dielectric drying methods with a suitable drying thickness for peanuts.