Carbon microcoils with coil diameter about 4μm, pitch about 0.5－0.8μm (A) and coil diameter about 20μm, pitch about 1－4μm (B) were prepared by a vapor phase catalytic cracking process. Paraffin wax/carbon microcoil composites were made by dispersing the latter in the former, which were sandwiched between epoxy glass plates and Nomex honeycomb plates. The complex permittivity (ε) and the complex permeability (μ) of the composites were measured at 8.2－12.4GHz by a reflection transmission system. Results show that the permittivity loss tangent of paraffin wax/B composites is higher than that of paraffin wax/A composites. A-coils show a better microwave absorbing property than B-coils. The microwave reflection loss of the sandwiched composites filled with A-coils is more than 10dB at the range of 10-15GHz, more than 5dB at the range of 4.6-18GHz and the maximum microwave reflection loss is 18dB at a frequency of 12.4GHz, which are opposite to the results expected from the loss tangent (tanδε＝ε″/ε′). It is assumed that A-coils with a smaller diameter and pitch have a higher chiral parameter (ξ) value. Moreover, the value of ξhas a greater impact on the microwave absorption than the εvalue for the carbon microcoils, which results in better microwave absorbing properties.
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