Electromagnetic absorption of sandwich panel made of glass fiber reinforced polymer and nanocomposite foam filled honeycomb

Sandwich panels were processed and characterized for electromagnetic absorption. The faces are made of glass fiber reinforced epoxy. The core of the panel is made of carbon nanotubes reinforced polymer foam filling a metallic honeycomb. Electromagnetic modeling and experimental characterization of the core showed that the honeycomb, acting as a hexagonal waveguide, improves the absorption properties in the GHz range above the cut-off frequency compared to the composite foam alone. The EM absorption can be tuned by changing the hybrid material properties. The required levels of electrical conductivity are attained owing to the dispersion of low amounts (1-2 wt%) of carbon nanotubes inside the polymer matrix. The combination of the foam and a honeycomb architecture contributes to the decrease of the real part of the relative effective permittivity R(ε_{r, eff}). Varying the cell shape of the honeycomb changes the frequency range for high absorption. The absorption properties of sandwich panels has been measured from 8 to 40 GHz and successfully compared to predictions from an analytical model developed for multilayered topologies. Our results show that a careful design of face-sheets allows to preserve and even improve the absorption performances of the hybrid in a dedicated frequency range.