The dielectric properties of tilapia at different parts (anterior, middle, tails, belly), different temperatures (10-90 ℃), different frequencies (300-3 000 MHz ), and different moisture contents (3.8590-0.1161 g/g d.b. (dry basis)) were determined using the coaxial line method. The dielectric constants of tilapia among four parts were similar, the greatest difference was 4.91, and the average difference was 2.37. Four parts of tilapia were the same in variation trend of dielectric loss, but the value of belly was lower than that of others. This is perhaps the fact that It is maybe the fat content of belly was higher than other parts. However, due to the differences were small, the effects of components on dielectric loss can be ignored. For this reason, the average of dielectric properties values(ε', ε") for four parts were employed to investigate the effect of temperature, frequency, moisture content on tilapia dielectric properties valuse (ε', ε"). In addition, the dielectric constant of tilapia decreased with the increase of frequency and temperature, and decreased along with the decrease of moisture content. However, with the increase of frequency, the dielectric loss decreased to a minimum (2 300 MHz) and then increased. When the frequency was lower than 2 300 MHz, dielectric loss increased as the temperature increased, and when the frequency was higher than 2 300 MHz, it was contrary. The dielectric loss also decreased with the decrease of moisture content. Moreover, the penetration depth[Frequency: 915, 2 450 MHz; Temperature: 10-90 ℃; Moisture content: 3.8590-0.1161 g/g d.b. (dry basis)] of tilapia was calculated, regression analysis was employed to develop polynomial equations of dielectric properties and penetration depth. The predicted values and the experimental values were well correlated.%采用同轴探针法在温度10～90℃、频率300～3 000MHz、干基水分含量3.8590～0.1161g/g d.b.的条件下对罗非鱼的介电特性值(介电常数ε',介电损失率ε″)进行了测定.结果显示,罗非鱼4个部位(前部、中部、尾部、腹部)的介电常数相近,最大部位差为4.91,平均部位差为2.37;4个部位介电损失率变化趋势相同,只有腹部的值偏小,这是由于腹部脂肪含量相较于其他部位稍高.但是由于这种差别微小,成分对介电损失率的影响可以忽略,所以本研究中以4个部位介电常数、介电损失率的平均值为指标,考察温度、频率、水分含量对罗非鱼介电特性值(ε′,ε″)的影响.温度一定时,介电常数随频率升高而降低；频率一定时,介电常数随温度升高而降低；温度和频率一定时,介电常数随水分含量的降低而急剧降低.频率的升高使得介电损失率呈先降低再升高趋势,在2 300 MHz附近出现拐点,拐点之前,介电损失率随温度的升高而升高,拐点之后,介电损失率随温度的升高而降低.介电损失率随着水分含量的降低而降低.可算得罗非鱼在915、2 450 MHz频率下,10～90℃,3.8590～0.1161g/g d.b.时的穿透深度,采用回归分析法得出罗非鱼介电特性值及穿透深度的回归预测方程,预测值与实验值呈良好的一致性.
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