Okamura (1981) presented the concept of measurement of
high grain moisture content at 9.4 GHz using specific
attenuation, which was defined as the ratio of the microwave
attenuation per unit length to the sample density (bulk
density). A prototype moisture meter using microwave
attenuation at 10.5 GHz and moisture density (defined as the
product of decimal moisture content and bulk density) was
also proposed (Kim et al., 2002).