Experimental Fabrication and Characterisation of Textile Metamaterial Structures for Microwave Applications

Abstract

This thesis presents an investigation of fabrication technologies and electromagnetic characterisation of textile metamaterials in the microwave frequency range. Interdisciplinary in nature, the work bridges textile design practice and electromagnetic engineering. The particular ambition was to explore a number of surface techniques prevalent in the textile design field, and map their suitability for the construction of metatextiles for microwave operation. Two different classes of metatextiles, all-dielectric and dielectric with electrically conductive patterns, were examined. First, five structures of all-dielectric textiles and papers are reported; three textiles with graded embroidered and screen printed patterns, and two papers embellished with regular and irregular laser cut patterns. Permittivities for these materials were measured in a purpose-built test chamber and shown to be similar to permittivity ranges exhibited by solid discrete metamaterial cells previously reported in the scientific literature. Importantly these metatextiles were realised within one textile surface and one fabrication process, bypassing the need to assemble large numbers of isotropic material cells. This reveals the potential for rapid and low-cost manufacture of graded textile materials to produce anisotropic ground plane cloaks. Secondly, three studies are presented that examine the use of electrically conductive patterned textile materials in the design of metatextiles which exhibit negative refractive index over a narrow frequency band. A range of e-textile (electronic textile) fabrication technologies were explored to assess their suitability for prototyping splitring and wire arrays, resonating in a narrow region between 3 - 10 GHz. Designs utilised a repeated unit cell pattern on a two-dimensional textile surface and were subsequently pleated into the required three-dimensional structure. A small negative refractive index was achieved for an embroidered prototype at 4.9 GHz, and two ‘printed and plated’ prototypes at, 7.5 GHz and 9.5 GHz respectively. In summary the thesis demonstrates a set of guidelines for the fabrication of textile metamaterials for microwave frequencies, derived through a practice-led and interdisciplinary method based on material experimentation.