Relationships between structure and microwave dielectric properties in cotton fabrics

Abstract

The microwave dielectric properties of cotton fabrics in the fabric thickness direction are investigated in relation to the fabric construction, thread count and solid volume fraction (SVF) under the five different relative humidity (RH) conditions. The dielectric constants of the fabric samples exhibits increasing trends with RH, and this is primarily due to more abundant free water in the samples. For most of woven and knitted samples, an increase in thread count results in a higher dielectric constant and this is associated with the increase in SVF. By comparing the woven and knitted samples of the same SVFs, it is found that the woven fabrics tend to have higher dielectric constants than the knitted samples at near 2.45 GHz. This observation of the dielectric properties of cotton fabrics clearly indicates that although the SVF is primarily responsible for the resulting dielectric properties of fabrics, other structural parameters must also be considered in dielectric analysis. Based on in-situ analysis of yarn orientations in the given samples, we claim that the yarn orientation plays an important role in the microwave dielectric properties of cotton fabrics.