The dielectric properties of cotton fabric, polyester fabric, and polyester/cotton blended fabrics with different moisture content (MC), grammage, and composition ratio were tested under 10-GHz microwave in free space. A uniform padder was developed to ensure a uniform distribution of moisture in the fabric. A power-law dielectric mixing model was then adopted and simplified to describe the MC dependence of the dielectric constant and dielectric loss factor. Two equivalent factors $K_{1}$ and $K_{2}$ , the values of which can be found in lookup tables based on surface-fitting results or calculated using regression equations taking the fabric grammage and the cotton percentage into accounting, are introduced to simplify the modeling. A prototype fabric moisture detector, consisting of a 10-GHz dielectric resonator-type oscillator, horn antenna, rectangular sample holder, detector, and digital voltmeter, was developed. A calibration equation, suitable for use in measuring the MC of cotton /polyester blended fabrics, is proposed and evaluated with different fabrics. Experimental results show that for MC in the range 0%–45% for cotton fabrics and for MC in the range 0%–35% for polyester/cotton fabrics, the coefficient of determination, the standard error of prediction, and the bias are all within acceptable ranges.

中文翻译：

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使用自由空间微波方法非接触式检测混纺织物中的水分含量

在自由空间10-GHz微波下测试了不同含水量（MC）、克重和成分比的棉织物、涤纶织物和涤棉混纺织物的介电性能。开发了一种均匀的轧花机，以确保织物中水分的均匀分布。然后采用并简化幂律介电混合模型来描述介电常数和介电损耗因子的 MC 依赖性。两个等效因子 $K_{1}$ 和 $K_{2}$ 的值可以在基于表面拟合结果的查找表中找到，也可以使用回归方程将织物克重和棉百分比计算在内，分别为为简化建模而引入。原型织物水分检测器，由 10 GHz 介质谐振器型振荡器、喇叭天线、开发了矩形样品架、检测器和数字电压表。提出了一种适用于测量棉/涤纶混纺织物的 MC 的校准方程，并针对不同的织物进行了评估。实验结果表明，棉织物的MC在0%~45%范围内，涤棉织物的MC在0%~35%范围内，确定系数、预测标准误和偏差均是在可接受的范围内。