Carbon nanocoil (CNC) is a carbon nanofiber with helical shape. In this study, we fabricated CNC-based composites endowed with electromagnetic wave absorption property. CNCs were synthesized by chemical vapor deposition using acetylene as a precursor and Fe and SnO2 particles as catalysts. The composites were produced by dispersing CNCs into epoxy resin or paraffin by ultrasonication, and then hardening a droplet of the solution on an aluminum substrate with ca. 2mm in specimen thickness. Paraffin was used as a solvent when producing the composites with the CNC concentration higher than or equal to 5wt.%; otherwise epoxy was used. The reflection ratio of the composites with different concentrations were measured by the free space method using lens antennas in frequency ranges of 5.6–40 and 67–110 GHz. The CNCs/epoxy composites of 0.1–1.0 wt.% showed poor reflection losses. The 10 wt.% CNCs/paraffin composite achieved a reflection loss of −32 dB at 79.2 GHz. Its bandwidth corresponding to the reflection loss below −20 dB was 4.85 GHz. The CNCs/paraffin composite also turned out to show a good absorption property in W band frequencies (75– 110 GHz).

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