On the use of low-cost metallic filaments for the fabrication of millimeter wave antennas

J. Castro¹, F. Pizarro¹, D. Vásquez^2* S. Bruna¹, M. Rodríguez¹

¹Pontificia Universidad Católica de Valparaíso, Escuela de Ingeniería Eléctrica, Valparaíso, Chile

²Pontificia Universidad Católica de Valparaíso, Escuela de Ingeniería Química, Valparaíso, Chile

*dreidy.vasquez@pucv.cl

Nowadays, communication devices are moving towards higher frequencies in the electromagnetic spectra, mostly on the named millimeter wave spectrum, mainly due to the need of the larger required bandwidth of the applications [1]. This increment of the operational frequency makes that prototypes becomes more expensive and difficult to implement due to reduce dimension of the topologies that are related to the wavelength in use. From that perspective, is that the use of 3D printing is getting a large interest for these applications, especially the low-cost solutions [2-4]. The aim of this work was the design, 3D printing fabrication, and characterization of 60GHz devices like pyramidal horn antenna, V-band and Ka-band waveguides by fused filament fabrication and posttreatment. The metallic filament was composed with polylactic acid and 90%wt copper and the pieces were printed with a low-cost custom 3D printer This printer features NEMA 17 0.9° motors and a 32-bit controller board with micro-step subdivision of up to 64 times, allowing to increase the printing resolution and a direct extrusion system. In addition, the used heatbreak is bimetal, which allows an easing melting of the materials with heat conduction up to 60% greater with respect to a single metal compound heatbreak [5]. Typically, 3D printers use brass nozzles due to their great compatibility of materials that can be use, added to its low cost, but have low resistance to mechanical abrasion. As the filament to use has over 90% copper particles, it is necessary to use another type of nozzle that has the capacity to withstand the abrasion. For this, a reinforced steel nozzle has been selected, highlighting its resistance properties to wear as its maximum operating temperature [6].

For the fabrication of the devices, an optimization of the printing parameters was performed. In the first attempt, the devices were printed with single thin walls however after sinterization step, they present very big holes due to the inhomogeneities of the filament. To overcome this problem and the high contraction that occurred during thermal treatments the antennas were printed scaled-up 113% and the waveguides of 115%. The final debinding was performed for more hours (11) and a lower heating rate than proposed by the manufacturer and the sintering cycle was executed in 3 steps: 25-480ºC at 8ºC/min, 480-1000ºC at 1.8ºC/min and 1000-1060ºC at 0.4ºC/min. The pieces contraction was around 8% while the densification measured by Archimedes' method was 70%. From porosity, 10% was open porosity while the closed porosity was interconnected. The inner surface roughness as-printed was Ra = 6.877 µm for the waveguide and Ra = 9.149 µm for the antenna while the result after sintering was Ra = 6.433 µm and Ra = 10. 417 µm, respectively. During thermal treatment, the pieces were embedded in alumina powder and carbon powder, as support material to create an anoxic environment to avoid copper oxidation, the XRD results were 95.6 %wt of copper, 2%wt of copper oxide, and 2.4%wt of silicon oxide. The measurement results of the gain radiation patterns of the antennas at 60 GHz showed a maximum gain Gmax of around 15 dB, which is in line with the simulated results at the same frequency. This result demonstrates that there are no important losses introduced either by mismatching, surface roughness, or conductivity of the sintered part. In addition, we can see that for the three printed samples, measurement results are very similar on both E- and H-planes, confirming the repeatability of the printing and sintering process proposed in this study. Finally, we can see an increment in the sidelobes of the E-plane, which can be explained due to the dimension tolerance after sintering.

References

[1] T. S. Rappaport, S. Sun, R. Mayzus, H. Zhao, Y. Azar, K. Wang, G. N. Wong, J. K. Schulz, M. Samimi, and F. Gutierrez. Millimeter wave mobile communications for 5g cellular: It will work! IEEE Access, 2013, 1:335–349.

[2] Y. Li, L. Ge, J. Wang, S. Da, D. Cao, J. Wang, and Y. Liu. 3-d printed high-gain wideband waveguide fed horn antenna arrays for millimeter-wave applications. IEEE Transactions on Antennas and Propagation, 2019, 67(5):2868–2877.

[3] A. C. Paolella, C. D. Fisher, C. Corey, D. Foster, and D. Silva-Saez. 3-d printed millimeter-wave lens systems at 39 ghz. IEEE Microwave and Wireless Components Letters, 2018, 28(6):464–466.

[4] F. Pizarro, R. Salazar, E. Rajo-Iglesias, M. Rodríguez, S. Fingerhuth, and G. Hermosilla. Parametric study of 3D additive printing parameters using conductive filaments on microwave topologies. IEEE Access, 2019, 7:106814–106823.

[5] slice engineering website. https://www.sliceengineering.com/. Accessed on: 2022-10-30.

[6] e3d website. https://e3d-online.com/products/v6-nozzles. Accessed on: 2022-10-30.

[7] The virtual foundry website. https://thevirtualfoundry.com/. Accessed on: 2022-10-30.