螺旋形炭纤维的吸波性能

通过气相催化裂解法分别制得了螺径约为4μm、螺距为0.5μm～0.8μm的炭纤维（简称为coils-A）和螺径为20μm左右、螺距为1μm～4μm的炭纤维（简称为coils-B）.以coils-A和coils-B为掺杂体与石蜡制成复合材料在8.2 GHz～124 GHz范围内通过反射传输系统测量其电磁参数,结果表明该等微米级螺旋形炭纤维磁损耗为零,其中coils-B的介电参数的虚部及其损耗正切值tanδε较coils-A的高.分别以coils-A和coils-B为手性掺杂体制得填充有手性材料的夹芯蜂窝板复合材料,研究发现coils-A的吸波效果较好,在10 GHz～15 GHz的范围内对电磁波的反射衰减量大于10 dB,在4.6 GHz～18 GHz 的范围内对电磁波的反射衰减量均大于5 dB,在12.4 GHz时最大的反射衰减量为18 dB,其结果与藉由电磁参数所预测的结果相反.经计算,coils-A的手性参数ξ较大.因此,手性参数ξ对于提高吸波性能的影响大于介电参数ε的影响.

The microwave absorbing properties of carbon microcoils

Carbon microcoils with coil diameter about 4 μm, pitch about 0.5-0.8 μm (A) and coil diameter about 20 μm, pitch about 1-4 μm (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 8.2-12.4 GHz 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 10 dB at the range of 10-15 GHz, more than 5 dB at the range of 4.6-18 GHz and the maximum microwave reflection loss is 18 dB at a frequency of 12.4 GHz, 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 ξ has a greater impact on the microwave absorption than the ε value for the carbon microcoils, which results in better microwave absorbing properties.