Synthesizing 3D Metamaterials for RF, Microwave and THz Applications

INTRODUCTION
The aim of this project is to design and fabricate 3D electromagnetic metamaterials, to be used as building blocks for applications ranging from visible to radio frequencies. The proposed structures will be the result of rapid and efficient Additive Manufacturing (AM) technologies utilizing appropriate materials, combined with surface functionalization methods, such as Electroplating or Sputter Deposition. This research is part of the larger "SYMETA" project and falls within the EPSRC "Microelectronic device technology" research area.
FABRICATION
A crucial factor in the design and fabrication process of metamaterials is the operating wavelength the application is aimed at. More specifically, the size of the 3D meta-atoms needs to be in the subwavelength scale of the operating wavelength. For that reason, there is a high demand for a set of fabrication techniques across all length scales of interest. The general concept is to have the 3D metamaterials built on a dielectric mold. In the mm-cm scale, one can take quite a few approaches, one of which is the print-and-paint methods. This is a two-step process, where the dielectric form is printed and then filled with conductive paint. In our case, ABS is used as dielectric and the conductive paint consists of copper particles and a binder. Alternatively, the dielectric and conductive parts can be printed simultaneously by using a multi-material printer, such as the voxel 8 model. PLA and ambiphilic silver nanoparticle inks are used. Finally, there is the option of printing solid silver conductors inside a low temperature sintering ceramic. The whole ensemble is fabricated on a glass substrate. The last method is still under development but can potentially reach a resolution in the micrometre scale. 3D printing methods are having a hard time reaching resolution in this scale, so this is crucial because it pushes the resolution limit even higher. Recent developments in 3D metamaterial manufacturing have successfully covered the surface of the metamaterial with a conductive material, e.g. Copper, in order to increase their electrical conductivity. Research on metamaterial should adress the potential of utilizing different technologies for manufacturing metamaterial-based devices.
CONCLUSIONS
The fabricated 3D metamaterials will be used as building blocks for manufacturing fully operational metamaterial devices operating from MHz to THz. Before anything else, a thoughtful study of the available materials, should take place, in order to cultivate a deep understanding of the matter at hand. The widely used CST Microwave Studio can provide invaluable insight about different geometries and arrangements between them. The greatest challenge of the project is the creation of functional prototypes from a size range between cm-micrometre. By the end of the project, we hope to have established a thorough fabrication process, in which 3D metamaterial-based devices can be efficiently and rapidly produced across all length scales of interest.