Processing and properties of polymer-based composites for metamaterials applications

• Main Author: Wang, Yunqi
• Other Authors: Grant, Patrick
• Published: University of Oxford 2015
• Subjects: 620.1
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.712425

Transformation optics offers a theoretical tool for the design of electromagnetic devices that can manipulate the flow of microwaves in an unprecedented way, but also places demanding requirements on the permittivity ε and permeability μ of materials used to form the devices, along with their spatial variations in three dimensions. Polymers that are light-weight and with high processability are considered potentially useful in realizing transformation optic designs, but only where the effective ε and μ can be increased controllably by loading the polymer with inorganic particles. This thesis focuses on the development of bespoke polymer-based composite materials and robust manufacturing approaches for potential applications in electromagnetic devices. Three main manufacturing approaches have been explored. Firstly, casting was demonstrated to produce bulk materials with equal permittivity and permeability by embedding NiZn ferrite particles in an epoxy matrix. Hybrid composites with a combination of soft magnetic ferrite and metallic magnetic fillers, anisotropic composites with magnetic field aligned fillers, and high magnetic anisotropic materials with multi-layered structures were all produced successfully. Developed materials showed superior electromagnetic properties to many competitor approaches for miniaturization and low profile antenna, especially for the case of magnetically anisotropic cast tiles. Secondly, a spray deposition approach was developed for the fabrication of large-scale nanocomposite polymer-based films. By incorporating Fe3O4 nanoparticles or multi-wall carbon nanotubes, as a thin sandwich layer into a perfluoroalkoxy (PFA) matrices respectively, 30-50 μm thick flexible multilayer nanocomposite films with enhanced dielectric and magnetic properties were produced. A broadband permittivity and permeability measurement technique was also developed for these films. Finally, a 3D printing technique was employed to produce electromagnetic materials with complex 3D shape. Feedstock on a ferrite/acrylonitrile butadiene styrene (ABS) composite filament was demonstrated successfully and may facilitate the realization of complex design transformation optics devices.