Superior EMI shielding performance of thermally stable carbon nanofiber/poly(ether-ketone) composites in 26.5–40 GHz frequency range

An electromagnetic radiation shielding material (ERSM) based on carbon nanofiber-reinforced poly(ether-ketone) composite was prepared via corotating twin screw extruder and then injection-molded into dog bone-shaped specimens for testing. In order to design this type of material ERSM, electrical conductivity was targeted as key property using a conducting inclusion, carbon nanofibers (CNFs). Electrical conductivity increased from ~10−13 S/cm for neat PEK to ~10−3 S/cm for samples having 14 vol % (20 wt%) of CNFs, which was close to the requirement for microwave shielding. Nanocomposites are shown to exhibit up to −40 dB (>99.999 % attenuation) of total shielding effectiveness at 14 vol % (20 wt%) loading in the frequency range of 26.5–40 GHz (Ka band). This formulation of nanocomposites (14 vol % loading) shows shielding effectiveness due to absorption of ~−37 dB with very less reflection loss of ~−3 dB in the prescribed frequency range. Achievement of such high absorption-dominant shielding effectiveness (−37 dB) along with high thermal stability (T0.25 ~ 614 °C) and mechanical strength (tensile strength ~112 MPa and tensile modulus ~7.2 GPa) substantiates its capability as light weight, thermally stable, and mechanically strong EMI shields for demanding applications such as aerospace, defense, and space applications.