基于微波干燥的黑莓介电特性研究

以黑莓为对象，利用网络分析仪测量并研究了频率（1～3 000 MHz）、黑莓含水率（20%～80%）和温度（20～100 ℃）对相对介电常数ε′和介质损耗因数ε″的影响；计算了微波穿透深度，并分析频率、含水率和温度对其的影响；建立了部分频率下黑莓介电参数与主要影响因素的关系模型，检验了基于介电参数预测含水率的精度和可行性。结果表明，在1～3 000 MHz频率段内，黑莓的介电常数ε′和介电损耗因子ε″都随频率的增大而减小；ε′随含水率的增大而增加，但随温度的增大而减小；ε″随含水率的增大而下降，但随温度的增大而增加；能量穿透深度随温度、频率的升高而降低，随含水率的升高而增加。可用二元二次方程描述介电参数和主要影响因素的关系，且各模型的决定系数皆大于0.96。所构建的模型可以很好地描述黑莓的介电参数与各主要影响因素的关系，说明基于介电参数和温度预测黑莓的含水率是可行的。

Dielectric properties of blackberries based on microwave drying

Dielectric properties of blackberries samples with 20%-80% w.b. moisture content were determined with a network analyzer and an open\|ended coaxial\|line probe over the frequency ranged from 1 to 3 000 MHz and the temperature ranged from 20 to 100 ℃. The effect of frequency， moisture content and temperature on the relative permittivity （ε′）and dielectric loss factor （ε″）were investigated， the penetration depth was measured， and the relation model of dielectric properties of blackberries and the main influence factors was established， in order to inspect the precision and feasibility of moisture content prediction based on dielectric parameter. The results showed that both ε′ and ε″ of blackberries decreased with increasing frequency. ε′ increased with increasing moisture content and decreased with increasing temperature， however， ε″ increased with increasing temperature but decreased with increasing moisture content. The penetration depth decreased with increasing temperature and frequency， but increased with increasing moisture content. The relationship between dielectric parameter and main influence factors could be described by binary quadratic equations， and the determination coefficients of each model were higher than 0.96， indicating that the model could well describe the relationship， thus it is feasible to predict the moisture content of blackberries based on dielectric parameters and temperature.