Study On Dielectric Properties Of Chestnut, Filbert Nut And Their Target Pests At Radio Frequency/microwave

With the practicing and further development of the policy of returning farmland to theimplementation, all over the country have began to develop dried fruit economic trees such aschestnut and filbert, but the main problems of postharvest of chestnut and filbert is the mothdamage. The traditional disinfestation is chemical fumigation, but with the potentiallydangerous in environment and human, and to meet the requirement of no chemical residue ofagricultural products, it has been provided this method will be disabled internationally inyears. At present there are much research to develop the substitution of chemical fumigation,and each method has its advantage, but for the bad treatment effect, the long processing time,adversing to product quality, the high cost of investment, and the need of specialized technicalpersonnel et al., so it is much difficult for promotion. A lot of studies have showed that thedielectric heating could be an effective disinfestation for postharvest agricultural products,and dielectric properties are determined by the measured frequency, temperature and moisturecontent. The dielectric properties of chestnut and filbert were studied to provide a safe andeasy disinfestation for the two nuts, and provided basic datas for developing instruments.The effect of frequency (10~4500MHz), temperature (20~60℃), and moisture content ondielectric properties of chestnut and filbert were studied with an open-ended coaxial prob andimpendance analyser. The influence of temperature and frequency to dielectric properties ofchestnut weevil was also studied, the internal mechanisms of these factors on the dielectricproperties and possibility of controling chestnut weevil in chestnuts with dielectric heatingwere researched. The main conclusions as follows:(1) For chestnut and filbert, the dielectric constant and loss factor decreased withincreasing frequency but increased with increasing temperature and moiature content, the lossfactor of filbert flour is much higher than that of compressed chestnut flour with the similarmoisture content at the same temperature and frequency.(2) The dielectric constant of chestnut weevil decreased with increasing frequency, andincreased with increasing temperature. The dielectric loss factor decreased with increasingfrequency, at any frequency, the loss factor increased with increasing temperature in less than1000MHz, but decreased in more than1000MHz.(3) Comparision of the loss factor of chestnut and chestnut weevil at commonly usedindustrial frequencies of27(RF) and915(MW) MHz showed that the loss factor of chestnut weevil was much higher than that of chesunut at27and915MHz, that mean chestnut weevildifferentially heated faster than chestnut, with the differentially heating reduced in MWheating when compared to RF heating.(4) Penetration depths at calculated for chestnut and the differential heating between thechestnut and cheatnut weevil suggested continuous industrial-scale RF treatment protocolscould be developed to disinfest these products.(5) Penetration depths of chestnut and filbert decreaed with increasing frequency,temperature and moisture content. And the Penetration depth at27MHz is much higher thanthat at915MHz, so it is impossible that the common frequency of27MHz can be used indisinfestion of chestnut and filbert.