2, Stratasys, Eden Prairie, Minnesota, United States
The possibility of using fused deposition modeling (FDM) to produce electromagnetic interference (EMI) shields may reduce drawbacks of current EMI shields made from sheet metal. These drawbacks include cost, weight, and freedom of design. However, the performance of these FDM-printed composite materials for EMI applications must first be assessed. Here, we focus on electrically conductive polymer composite parts made via FDM. In this work, we directly compare compounded samples of the most common polymer EMI shielding composite formulations found in the literature, including graphite, stainless steel, Ni-coated carbon fibers, and Ni-coated carbon nanotube fillers. Additionally, in order to examine the influence of structural print parameters, studied samples consist of a variety of relative print orientations (45° and 90°) and thicknesses (2mm, 6mm, and 1cm). Because electrical conductivity is a main characteristic of successful EMI shields, we test the electrical properties of these various polymer-matrix composite materials via both DC and AC methods in order to assess their shielding effectiveness. First, we measure the individual FDM filament samples and printed parts via DC conductivity measurements. Conductive sample contacts are made by using sputtered metallic contacts and metallic paint, and the measured electrical resistance is converted to electrical resistivity. For AC measurements, we conduct testing of the electromagnetic interference shielding effectiveness as a function of frequency. AC fields are emitted and received through sample sheets using a spectrum analyzer and two loop antennas. Preliminary results show that the Ni-coated carbon nanotubes and the graphite samples show the most optimal characteristics for EMI shielding, while the stainless steel samples also show promising performance. Results also show that varying print orientation does have an effect on the performance of the printed parts.