Study On Non-destructive Detection Of Rice Moisture Content Based On Dielectric Properties

Water content affects rice quality,which also has an important impact on rice storage,transportation,acquisition and processing.The measurement accuracy of water content detection technology based on dielectric characteristics is not ideal affecting by many factors.In this paper,the relative dielectric constant(ε′)and dielectric loss factor(ε")of rice were measured by the dielectric characteristic detection system composed of the test probe and impedance analyzer.The effects of test probe structure,frequency,temperature,the the mathematical modeling method on measuring precision were studied,As well as the theoretical analysis and experimental verification were carried out.The main results and conclusions are as follows:1)The electric field distribution of the test probe was simulated based on ANSYS,And the effect of the structural form and parameters of the test probe on detection performance were studied.The results show that the concentric cylindrical probe with axial grounding protection plate has better performance.Taking the length of the inner plate,the distance between the plates,the length of the protective plate and the gap as experimental factors,the sensitivity and edge effect are taken as experimental indexes.orthogonal test method was used to optimize and design the structural parameters of the test prob.2)The effects of moisture content and frequency on relative dielectric constant and dielectric loss factor were studied.The research results showed that the relative dielectric constant decreased with the increase of the measurement frequency between 1k Hz and 1 MHz,When the frequency is greater than 300 k Hz,the dielectric loss factor decreased with the increase of frequency and increased with the increase of water content.The measurement frequency and moisture content had a obvious effect on the dielectric properties of rice.The prediction accuracy of water content prediction model established with different dielectric parameters at different frequencies was analyzed.The results show that the support vector machine regression model based on the combination of relative dielectric constant and dielectric loss factor and successive projection algorithm gave the highest correlation coefficient of predication set(0.980)and the lowest root mean square error of predication set(0.403%).3)The effects of temperatures and frequency on relative dielectric constant and dielectric loss factor were studied.The least square method was used for linear regression of predicted moisture content and measured moisture content at different temperatures and the temperature compensation was carried out for the prediction results.The performances of the best model to predict different varieties rice moisture content was explored to determine the applicability of the model.When the best model was used to predict the water content of different varieties of rice,the prediction results are more accurate.Compared with the actual water content measured by the drying method,the prediction error was concentrated within ±0.5%.The study provided a new idea for improving the accuracy of the grain moisture detection device.