Extrusion freeforming of millimeter wave electromagnetic bandgap (EBG) structures

Purpose - The aim of this paper is to provide an easy method of extrusion freeforming to fabricate microwave electromagnetic bandgap (EBG) crystals. EBG crystals are periodic dielectric structures that can block wave propagation and generate a bandgap. These crystals can be used in high capability antennae, electromagnetic wave semiconductors, micro resonators, high-reflectivity mirrors and polarizing beam splitters. Design/methodology/approach - The effects of extrusion process parameters and paste characteristics were investigated. Finally, one-period and two-period woodpile EBG crystals with bandgaps in the frequency region of 90-110 GHz were fabricated and the bandgap was measured. Findings - The filament diameter is influenced by whether extrusion is carded out with or without a substrate and by the free fall-distance from the nozzle. The quality of lattice structures is dependent on paste flow and properties. A ceramic paste with 60 vol. % (the fraction of ceramic powder based on solvent-free polymer) was well suited to fabrication. The solvent content also influenced the fabrication. The experimental results show that under similar to 12 per cent solvent mass fraction in the paste and relatively high extrusion ram velocity (more than 0.014 mm/s) at a pressure of 14 MPa, samples with high quality were fabricated. Originality/value - This paper demonstrates that the rapid prototyping method of extrusion freeforming can be applied for the fabrication of EBG crystals from ceramic powders and the important factors which influence the product quality are identified.