Abstract:

Objective For detecting the moisture content of fabric accurately, it is critical to understanding the relationship between moisture content and dielectric constant of fabrics. The objective of this study is to establish the relationship between moisture content and dielectric constant for two-component fabrics with different materials, thicknesses and component ratios, aiming for accurate measurement of moisture content in different types of textiles.

Method Based on the Bruggeman-Hanai dielectric mixing model, the relationship between the dielectric constant model of water content of two-component fabric was developed by considering the influence of fabric thickness and the pro-portion of multi-component fabric components under different material, thickness and component ratio was obtained. The dielectric constant measurement experiments of cotton, chemical fiber and blended fabric with uniform humidity were carried out, and the coefficient of the dielectric constant model of the two-component fabric was obtained.

Results For the theoretical prediction model, when the depolarization factor coefficient of pure cotton fabric L₁=0.35 and the depolarization factor coefficient of chemical fiber fabric L₂=0.23, the comparison results of the moisture content prediction model of pure cotton and chemical fiber cloth and experimental data were able to be obtained. The root mean square error(RMSE)calculation was carried out and it was found that the theoretical model RMSE of different fabric materials was less than 3%, and hence the prediction on the relationship between moisture content and dielectric constant, for pure cotton and chemical fiber fabrics, was proven reliable. When the cotton fabric coefficient C1 (the ratio of the thickness coefficient of pure cotton fabric to its thickness) was 1.475, B1 (the correction factor for pure cotton fabric)was 0.683 3; and when polyester fiber fabric C2 (the ratio of the thickness coefficient of blending textiles to their thickness)was 1.567, and B2(the correction factor for synthetic fabrics) was 0.743 2. For cotton fabrics, the RMSE ≤4.6%. Comparison of the prediction results of the model to the experimental results showed that the model enabled a good prediction on the permittivity related to the thickness of cotton fabrics. For chemical fiber fabrics where RMSE ≤ 3.8%, the prediction of fabrics with larger thickness and lower moisture content was not as good. However, when the moisture content of the fabric was greater than 3%, the prediction was generally better. When the determinant of blended fabric α =0.67, for fabrics with cotton content between 20%-35%, the prediction results of the two-component fabric theoretical model were close to the experimental results, and the prediction was better.

Conclusion In order to accurately measure the moisture content of fabrics with different materials, varying thickness and diversified components, this research explores the influence of changes in fabric material, thickness and composition ratio on moisture content and permittivity based on the microwave resonator method, and then establishes a theoretical model of fabric moisture content permittivity. After comparing and analyzing the predicted value of the model and the experimental value, results show that the model has good prediction accuracy, the RMSE is less than 5%.

Key words: fabric, moisture content, resonant cavity, dielectric constant, mathematical model