Dielectric constants of sewed multilayer fabric for wearable e-textiles

Wearable antennas are usually designed and manufactured according to the selected substrates and then sewed into regular clothing in real-life applications. For some antennas, which their radiation and the ground plane are on the same side of the dielectric substrate, two-layer substrates made of the original substrate and additional clothing change its dielectric properties and further affect their performance. Previous works only demonstrate that single-layer fabric substrate has an effect on the design and properties of the certain antennas. However, dielectric properties of sewed multilayer fabrics have not been reported. In this work, the influence of the number of parallel sewing threads within 120 mm in the fabric along single direction (referred to as sewing threads trace distribution density) and sewing directions on dielectric properties of single-layer fabric are explored first. Next, the dependence of dielectric properties of sewed multilayer fabric on their components' arrangement and volume fraction is mainly investigated. Common denim and nonwoven were used as samples. Sewed multilayer fabrics with different arrangement and volume fraction were fabricated, and their dielectric constants were measured by the split post dielectric resonators at 1.11 GHz. The results showed that sewing threads trace distribution densities, and sewing directions had little influence on the dielectric properties of single-layer fabric, whereas dielectric constants of sewed multilayer fabrics varied from their components' volume fraction regardless of their laying. Furthermore, a parallel mixing model was built to describe the dielectric behavior, and the results showed that it agreed well with the experimental results.