Multilayered foam-based electromagnetic interference absorber mimicking free space between pyramid structures

Abstract

In this study, we propose a multilayered foam-based electromagnetic interference (EMI) absorber that mimics the gradient of free-space structure found between conventional pyramid-shaped absorbers. To achieve this, conductive foams with different open cell sizes and multi-wall carbon nanotubes (MWCNTs) concentrations were sequentially stacked to form a composite structure, and a highly reflective conductive film was introduced at the bottom. This design strategy enables gradual impedance matching from the surface and promotes multiple internal reflections within the foam structure, thereby significantly enhancing the absorption of incident electromagnetic waves at the X-band frequency range (8.2–12.4 GHz). We systematically investigated the influence of foam thickness, MWCNTs concentration, cell size, and their stacking order on the total shielding effectiveness (EMI SE), as well as on its absorption and reflection components. While EMI SE was relatively unaffected by stacking sequence, the energy dissipation pathways could be precisely tuned, favoring either absorption or reflection. Notably, the structure with a gradient from large to small cell sizes, combined with a conductive film, achieved over 40 dB of EMI SE at 12.4 GHz, primarily driven by absorption. The results demonstrated that spatial control of foam cell structure and integration of reflective layers provide an effective route for high-performance, absorption-dominant EMI shielding. This approach offers a scalable, lightweight solution for next-generation EMI management in electronics and communication systems.