Microwave Permittivity of Micro-coiled Chiral Carbon Fibers

The microwave permittivity of micro-coiled chiral carbon fibers and straight carbon nanotubes suspended in paraffin wax was studied at the frequency range of 8.2-12.4GHz. The micro-coiled chiral carbon fibers were synthesized by the chemical vapor deposition. The straight carbon nanotubes were prepared by catalytic decompose of benzene using the floating transition method. The dissipation factors of the micro-coiled chiral carbon fibers are high at the microwave frequencies. The e' and e of the micro-coiled chiral carbon fibers decrease with frequency at the frequency range of 8.2-12.4GHz. The promising features of micro-coiled chiral carbon fibers would be due to their micro-coiling morphology. The e and tgδ of the large-coiled carbon fibers are higher than those of the small-coiled carbon fibers. Although the e' and e of the straight carbon nanotubes are much higher than those of the micro-coiled chiral carbon fibers, their dissipation factor tgS is much less than that of the large-coiled chiral carbon fibers. The tgδ of the large-coiled carbon fibers and small-coiled carbon fibers is 0.77-0.80 and 0.47-0.53 respectively, the straight carbon nanotubes, 0.45-0.77. The micro-coiled chiral carbon fiber would be a promising candidate as a novel microwave absorbent, especially in the GHz region, because of its micro-coiling morphology (microwave chirality). And microwave chirality is related to the size and microstructure of the micro-coiled chiral carbon fibers.