Achieving sub-wavelength spatial variations in the relative permittivity εr and permeability μr to control the propagation of the electromagnetic radiation opens up many opportunities for the development of new devices with improved or novel functionality . However, while the progress in Transformational Optics (TO) theory continues to suggest many beneficial designs and functions, the application of this principle in practice has remained complicated due to the difficulty of fabricating structures with the required controlled spatial distribution of permittivity and/or permeability. Rapid development of additive manufacturing and related 3D printing techniques have shown how these approaches might reduce the production time and simplify the manufacturing process of materials and devices with the required control of the spatial distribution of properties . 3D printing offers a flexible and scalable capability for the fabrication of objects with a complex form factor and may provide significant contrast variations in the refractive index . Our recent achievements in the formulation and fabrication of feedstock filaments with high dielectric permittivity for FDM 3D printing  allows convenient implementation of the principles of transformation electromagnetics for the design and fabrication of several types of optical devices to be operated in the microwave frequency band. In this work, we summarize our recent progress in design, fabrication, and characterization of several electromagnetic devices able to manipulate the propagated wave through a spatially graded refractive index. Four all-dielectric devices such as a metamaterial tunable absorber, a gradient refractive index lens, a spiral phase plate and a quarter-wave phase plate were all 3D printed using fused deposition modeling and our bespoke feedstock composite filaments with dielectric permittivity in the range 7 to 11. Although these optical elements were designed mainly to operate at a single frequency of 15 GHz, they show good capability over the broader frequency range of 12–18 GHz. Despite their relative simplicity, the experimental realization of these RF devices shows that there is a significant opportunity for 3D printing to enable TO-inspired devices in the microwave domain, especially as higher dielectric constant materials suitable for 3D printing become available.  J. B. Pendry, D. Schurig and D. R. Smith, Science, 312, 1780 (2006).  P. S. Grant, F .Castles, Q. Lei, et al, Philos. Trans. R. Soc. A. 373, 20140353 (2015).  D. Isakov, C. J. Stevens, F. Castles, P. S. Grant, Adv. Mater. Technol. 1600072 (2016).  Y. Wu, D. Isakov, P. S. Grant, Materials 10, 1218 (2017).
Journal: TechConnect Briefs
Volume: 4, Informatics, Electronics and Microsystems: TechConnect Briefs 2018
Published: May 13, 2018
Pages: 92 - 95
Industry sector: Advanced Materials & Manufacturing
Topic: 3D Printing