Fused filament fabrication of functionally graded polymer composites with variable relative permittivity for microwave devices

Fused filament fabrication (FFF) is a continuously growing additive manufacturing technology that aside from physical prototypes can also deliver functional prototypes and devices for radiofrequency (RF) and microwave applications. The very recent introduction of high-permittivity filaments for FFF has been one of the main facilitators for this major advancement, aiding microwave engineers to realise academics concepts that have thus far been impossible to fabricate and therefore invent new designs. However, the value to the RF community of these devices depends on accurate knowledge and repeatability of the electromagnetic properties of the materials being used which strongly relies on the processing strategy used during printing. This paper investigates the use of a high-permittivity filament and studies the impact of layer height and infill density on the relative permittivity (er) and loss tangent (tanS). A maximum relative permittivity of er = 9.63 +/- 0.16 and tanS = 0.003 +/- 0.0003 was achieved with a 200 mu m layer thickness and 100% infill density. Finally, the results of this study are used in designing, simulating, 3D printing and measuring the performance of a novel graded-index dielectric lens operating at 10 GHz. (c) 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).