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 8.2similar to12.4GHz. 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 epsilon' and epsilon" of the micro-coiled chiral carbon fibers decrease with frequency at the frequency range of 8.2similar to12.4GHz. The promising features of micro-coiled chiral carbon fibers would be due to their micro-coiling morphology. The epsilon" and tgdelta of the large-coiled carbon fibers are higher than those of the small-coiled carbon fibers. Although the epsilon' and epsilon" of the straight carbon nanotubes are much higher than those of the micro-coiled chiral carbon fibers, their dissipation factor tgdelta is much less than that of the large-coiled chiral carbon fibers. The tgdelta of the large-coiled carbon fibers and small-coiled carbon fibers is 0.77similar to0.80 and 0.47similar to0.53 respectively, the straight carbon nanotubes, 0.45similar to0.77. 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.