Microwave Dielectric Properties of Shelled and Unshelled Peanuts

Dielectric properties of shelled and unshelled peanuts were measured with a free-space-transmission techniqueat room temperature (23C) between 2 and 18 GHz, over wide ranges of bulk density and moisture content. For betteraccuracy, a pair of horn/lens antennas providing a focused beam was used, the sample was placed in a tunnel-shapedenclosure made of radiation-absorbing material to isolate it from surroundings, the sample thickness was selected to keepthe attenuation between 10 dB and the maximum attenuation measurable by the vector network analyzer (VNA), andtime-domain gating was applied to the main response. Typical variations of the dielectric properties with bulk density andmoisture content are shown at 8 GHz and 23C. Data, normalized to the lowest bulk density for each sample with the Landauand Lifshitz, Looyenga mixture equation, are tabulated for frequency ranges over which data of high validity were obtained.