scope:

Purpose and scope

These data are provided for use in the design of equipment for radiofrequency (RF) or microwave dielectric heating applications, for applications in grain and seed moisture measurement by electrical methods, and for use in the development of other capacitive or RF energy-absorption sensing devices. The data are also useful in predicting the dielectric heating behavior of grain and seed subjected to high frequency and microwave electromagnetic fields.

Frequency ranges for which detailed dielectric-properties data are available on several kinds of grain and seed include those from 1 to 50 MHz and 250 Hz to 20 kHz, and such data are provided over a range of moisture contents for some materials. Wide-frequency-range data (250 Hz to 12 GHz) are available on only a few commodities. Data for this wide frequency range are presented graphically when dependence on moisture content is also known. Tabular data are provided for single moisture contents on some commodities. Dependence of the dielectric properties of grain and seed on temperature is not well documented, and the only information included relates to shelled corn. An equation is included that takes into account changes in the dielectric constant of a given grain or seed lot that result from a change in bulk density. The dielectric properties presented are given with particular wet-basis moisture contents and test weights, when available. Although most values are for specific varieties and origins, these data are believed to be representative, and crop origin is of minor significance. With materials as variable as grain and seed, some deviation from listed values can be expected in dielectric properties of particular lots, even though moisture content, test weight, and bulk density may be similar.