Conductive 3D printing: resistivity dependence upon infill pattern and application to EMI shielding

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 $0.229\,\Omega {\text{m}}$ than the resistivity of $0.458\,\Omega {\text{m}}$ 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 $17.5\,{\text{dB}}/{\text{g}}\,{\text{cm}}^{3}$ at an infill density of 50% and would be the infill pattern of choice in an application constrained by weight or material.