Study On Dielectric Properties Of Coarse Cereals And Their Relationships With Main Influencing Factor

Grain is one of important agricultural products and basic materials of people’s life. Themoisture content of grain is a most significant target of evaluating it’s quality and selectingprocessing conditions. Currently, some researches have been conducted on moisture contentof grain in China and abroad, but these methods have several shortcomings such as long-timeexamination, expensive price and bulk size, so it isn’t suitable for large-scale. Comparing withthe traditional testing methods, predicating moisture content of grain based on dielectricproperties, resulted in advantages such as low cost, less time-consuming and easy toimplement continuous measurement. This paper, mainly through the study on dielectricproperties of coarse cereals and their relationships with influencing factors, will provide basisreference with exploitation of moisture meter for grain.In this thesis, using the flat electrode technology based on LCR meter, pearl barley,broomcorn, buckwheat and oat were used to study the influence of frequency (1k~1MHz),moisture content (11~23%), temperature (5~40℃) and bulk density(670~890kg/m3) on therelative dielectric properties. The reason why the dielectric parameters changed with thesefactors was analyzed theoretically. Furthermore, the mathematical models for predicatingdielectric parameters and moisture content of coarse cereals were established and verified.The conclusions are as follows:(1) The dielectric constant and loss factor of pearl barley, broomcorn, buckwheat and oatdecreased with increasing frequency over the frequency range from1k to1MHz. Comparingwith high frequency, the dielectric parameters reduced more evidently at low frequency. Atthe same frequency, higher temperature caused higher dielectric parematers. But in the rangeof frequency, temperature didn’t change the variation that the dielectric parameters decreasedwith increasing frequency.(2) When the temperature was the same, the dielectric parameters of pearl barley,broomcorn, buckwheat and oat increased as increasing moisture content, and the variation isthe same at different temperatures. The same moisture content, the higher temperature causesthe higher dielectric parameters. The dielectric constant value hasn’t changed with increasingmoisture content at different temperatures, but the dielectric loss factor increased.(3) At different frequency, the dielectric constant and loss factor of pearl barley, broomcorn, buckwheat and oat increased as increasing temperature, and the dielectricparameters increased most significantly with higher moisture content. Under the sametemperature, the dielectric parameters increased as increasing moisture content. But over therange of samples’ moisture content, moisture content doesn’t change the variation that thedielectric parameters increased with increasing temperature.(4) At different moisture content, the dielectric parameters of prarl barley, broomcorn,buckwheat and oat increased monotonically as increasing bulk density. Compared with lowmoisture content, viariance and velocity of variation is higher at high moisture content.(5) The influence of bulk density on dielectric parameters wasn’t siginificant. Therefore,the mathematical models of dielectric parameters, moisture content and temperature at10,50,100,500k and1MHz was established(P＜0.0001，R2＞0.96). Validation experiments showthat Obvious linear relationship was observed between measured dielectric parameters andcalculated dielectric parameters, R2＞0.96.(6) The three-factors and two-factors mathematical models for predicating moisturecontent of buckwheat, broomcorn and pearl barley, oat at10,50,100,500k and1MHz wasestablished(P＜0.0001，R2＞0.93). The coefficient of determination of measured moisture andcalculated moisture is all greater than0.95. The results show that measuring moisture contentof coarse cereals based on dielectric properties is accurate and feasible.