Conductive 3D printing: resistivity dependence upon infill pattern and application to EMI shielding
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Conductive 3D printing: resistivity dependence upon infill pattern and application to EMI shielding Logan Truman1 · Emily Whitwam1 · Brittany B. Nelson‑Cheeseman1 · Lucas J. Koerner2 Received: 8 April 2020 / Accepted: 8 July 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Polymers filled with conductive carbon black allow for the 3D printing of electrically conductive samples. The resistivity of these 3D printed samples depends on both the microscopic parameters of the carbon black filler and also on the macroscopic arrangement of the extrudites that build up the 3D printed sample. To investigate this dependence, we characterize the resistivity of five different printing infill patterns and find that a cross-ply pattern, which has extrudites oriented both in the direction of current flow and perpendicular to the direction of current flow has a lower resistivity of 0.229 Ωm than the resistivity of 0.458 Ωm found for a uni-ply pattern with all extrudites oriented in the direction of current flow. A Monte Carlo simulation of a large network of variable resistors illustrates the feasibility that the lower resistivity of the cross-ply pattern is caused by cross-flow which diverts current around areas of high local resistance. The same type of 3D printed conductive samples are tested as electromagnetic shields at frequencies up to 3.0 GHz using a custom-designed flanged coaxial sample holder. The shielding effectiveness of three sample infill patterns and four sample infill densities is compared. Cross-ply and angle-ply samples show the most efficient shielding effectiveness (normalized to sample density) of 17.5 dB∕g cm3 at an infill density of 50% and would be the infill pattern of choice in an application constrained by weight or material.
1 Introduction 3D printing allows for rapid prototyping by constructing three-dimensional objects directly from a computer model without the need for molds (plastics) or subtractive machining (metals). Fused filament fabrication (FFF), a common 3D printing method, builds the final material layer-by-layer using a thermoplastic filament that is extruded through a heated nozzle which is scanned through the physical points where material is to be added. Thermoplastic filaments used in the FFF process are typically electrical insulators; however, 3D printed conductive materials may benefit applications, such as flexible/wearable electronics, rapid prototyping of electronics, and electrical shielding enclosures. Conductive filaments for 3D printing that consist of a polymer matrix with carbon black (CB) filler to add electrical conductivity are commercially available [1, 2] and have * Lucas J. Koerner [email protected] 1
Department of Mechanical Engineering, University of St. Thomas, St. Paul, MN 55105, USA
Department of Electrical and Computer Engineering, University of St. Thomas, St. Paul, MN 55105, USA
2
been demonstrated in a variety of applications. An early demonstration of 3D printing conductive materials used polycaprolacto
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