Adjustment of the microwave dielectric function {epsilon'/[epsilon'(a f epsilon' - epsilon']} to estimate the moisture content of commom bean seeds at radiofrequencies

摘要

> face="Verdana" size="2">The development of universal dielectric models to estimate the moisture content of grains and seeds is one of the main trends in the field of engineering for the production of on-line moisture meter prototypes. These models allow the use of a single algorithm, derived from a unique calibration equation, to calculate moisture content of moving grain independently of bulk density or mass flow rate. In this paper, the performance of a dielectric model originally developed for microwave frequencies has been assessed for estimating moisture content of common bean seeds at radiofrequencies. The model was derived from the following function, face="Symbol">z = F{ face="Symbol">e"/[ face="Symbol">e'(a_f face="Symbol">e'- face="Symbol">e"]}, in which face="Symbol">e' e face="Symbol">e" are the relative permittivity and dielectric loss factor, respectively, and af is an extrinsic parameter dependent on the frequency of oscillation. Measurement of dielectric parameters was performed using samples varying in moisture content from 11.5 to 20.6% w.b., and bulk densities in the range from 756 e 854 kg m-3. The adaptation to radiofrequencies of a microwave dielectric model derived from the density independent function face="Symbol">z produced a model capable of estimating the moisture content (w.b.) of common bean seeds with a standard error of estimate and maximum error of 0.6 and 1.4 percentage points.